7 Coding Changes You Can’t Ignore When Migrating to SAP Cloud ERP (S/4HANA)

For many organisations, migrating from SAP ECC to SAP Cloud ERP (S/4HANA) is no longer a future ambition. It is an immediate commercial and compliance challenge. Delays increase risk. Custom code complexity inflates cost. And every workaround makes the next upgrade harder.

The case for Cloud ERP (S/4HANA) is well understood. The challenge lies in execution. The technical demands of migration are exacting and they leave little room for legacy thinking. In most programmes, close to 60% of custom ABAP code requires change. That alone makes coding decisions one of the clearest predictors of whether a migration holds up in the long term.

In this blog, we outline the seven coding changes that matter most. Ignore them and risk instability, rework and rising support effort. Address them properly and you lay the foundations for a Cloud ERP (S/4HANA) landscape that is fit for what comes next.

#1 Manual code remediation remains unavoidable for complex legacy logic

No matter how capable the tooling is, some ECC code simply cannot be converted automatically. Manual remediation is still required where legacy design choices clash with Cloud ERP (S/4HANA) expectations, including:

Complex, tightly coupled business logic
Custom Z-programmes built around obsolete modules
Enhancements with unclear ownership or documentation
Code written before modern Cloud ERP (S/4HANA) design standards were even considered

This work is costly and time intensive. It also carries risk when governance is weak. Rushed manual changes often introduce new defects or create performance problems that surface later, when fixes are more disruptive.

At the leadership level, the biggest risk is misjudging the effort involved. Manual remediation does not scale predictably. Timelines slip and costs escalate quickly when development teams are brought in late or asked to work without agreed standards.

The objective is not to remove manual remediation altogether; that is rarely realistic. The priority is to contain it. Focus manual effort on genuinely high value logic and prevent it from becoming the primary source of cost and delay.

#2 Automated remediation delivers faster results with lower risk

Automation has reshaped how organisations tackle Cloud ERP (S/4HANA) code conversion. Modern remediation tools can now deal with a large proportion of technical changes automatically, including:

HANA optimised SQL syntax updates
Deprecated function and object replacement
Data model adjustments and field changes
Identification and removal of unused code

For large landscapes, automation can reduce remediation effort by up to 90%. What once took months can now be assessed in days.

This shift changes how developers spend their time. Instead of working through repetitive technical fixes, they focus on validating results and resolving genuinely complex logic. The outcome is higher code quality and shorter delivery timelines.

When applied properly, automation is one of the most reliable ways to keep costs under control and reduce reliance on scarce ABAP skills. It also makes migration planning far more predictable, which matters just as much as speed.

#3 Custom code placement decisions shape long term cost and agility

One of the most consequential decisions in a Cloud ERP (S/4HANA) migration is where custom code should sit. Organisations now have several viable options:

Retain code in the Cloud ERP (S/4HANA) core
Move extensions to ABAP Cloud on SAP BTP
Rebuild logic as cloud native microservices
Replace selected functionality with specialist platforms

Each option has long term consequences. Keeping code in the core is straightforward, but it increases exposure during upgrades. ABAP Cloud enforces cleaner standards, though it demands new skills and ways of working. Microservices introduce flexibility but only organisations with strong architectural discipline tend to realise the benefits.

More mature programmes take a segmented approach. Mission critical processes remain in the core. Logic that changes frequently is pushed to the cloud. Reporting and integrations are handled outside the ERP, where they are easier to adapt without disrupting the core system.

This is where strong SAP support services make a material difference. They help organisations apply consistent governance to these decisions, rather than allowing short term delivery pressures to hard code long term technical debt.

#4 Integration architecture must modernise beyond SAP PI/PO

Many ECC landscapes still depend on SAP PI/PO as the backbone for integration. That approach no longer aligns with how modern SAP environments operate.

With PI/PO nearing the end of maintenance, change is unavoidable. More fundamentally, tightly coupled, point to point integrations create brittle landscapes. They make change slower, raise operational risk and complicate future system evolution.

Modern integration architectures look very different. They are:

API led rather than tightly bound to internal structures
Event driven rather than dependent on heavy batch processing
Cloud native rather than restricted by on-premise constraints

SAP BTP Integration Suite offers a clear strategic route for many organisations. In hybrid or multi cloud environments, alternative platforms may also be appropriate. The key is intent: integrations should be designed to absorb change, not resist it.

#5 The shift from SAP GUI to Fiori requires pragmatic prioritisation

SAP GUI is not disappearing overnight. Many transactions will remain in use for some time however, Fiori is now the strategic user interface for Cloud ERP (S/4HANA).

Native Fiori applications provide clear advantages, including:

Role based access
Improved usability
Embedded analytics
Mobile readiness

That said, not every SAP GUI transaction has a native Fiori equivalent. Wrapping GUI transactions in Fiori tiles preserves continuity but it does not deliver the same user experience as a purpose built app.

The sensible approach is selective investment. High volume and customer facing processes justify the effort required for native Fiori adoption. Low use or administrative transactions can remain as wrapped GUI tiles without undermining overall value.

This approach supports user adoption while keeping spend under control and avoids unnecessary complexity in areas that offer limited return.

#6 Transaction replacements demand early visibility and user readiness

S/4HANA simplifies the transaction landscape aggressively. Hundreds of ECC transaction codes are removed, merged or replaced, often with little room for backward compatibility.

A familiar example is the Business Partner model. Customers, vendors and contacts are no longer managed as separate objects. They are handled through a single, role driven transaction. The impact is significant:

Custom programmes calling obsolete transactions will no longer work
Users must adapt to new navigation paths
Training and structured change management become essential

There is a clear upside. Many organisations use this transition to cut back transaction sprawl and retire processes that no longer serve a useful purpose.

Timing matters. Teams that delay transaction mapping frequently encounter avoidable disruption during testing and go live. Early visibility allows technical fixes, user preparation and process decisions to happen in a controlled way.

#7 Z-transaction rationalisation reduces risk and supports a clean core

Z-transactions often reflect years of accumulated technical debt. Some were created to compensate for gaps that standard SAP has since closed. Others remain simply because their original rationale has never been challenged.

Rationalisation does not need to be complex:

Review actual usage, not assumed importance
Confirm business value with process owners

Replace with standard functionality where possible
Refactor only what genuinely differentiates the business

Each Z-transaction removed reduces ongoing maintenance, simplifies security design and improves upgrade resilience. Just as importantly, it brings the landscape closer to SAP’s clean core principles and lowers the cost of change over time.

Closing Thoughts

A Cloud ERP (S/4HANA) migration is not defined by the technical conversion alone. It is shaped by the choices made around custom code and how deliberately those choices are governed.

Organisations that succeed treat code as a strategic asset. They challenge what is carried forward, modernise what genuinely matters and apply discipline to how change is introduced and controlled.

With the right approach, complexity becomes manageable. Risk is identified early rather than discovered late. And the migration becomes a platform for sustained improvement, not simply another system change.

If you are planning your Cloud ERP (S/4HANA) journey, speak with specialists who understand both the technical and operational realities. Or explore how SAP support services can help reduce risk, limit disruption and keep your programme on course.