Customized ServiceNow instances require more deliberate preparation before each release than out-of-box deployments. The more an instance has been tailored to specific business needs, the more surface area there is for upgrade conflicts. Here is how to prepare effectively.
Understand your customization landscape before anything else
Many organizations do not have a complete picture of what has been customized in their instance and why. Before preparing for a release, invest time in cataloguing all modifications to out-of-box records, all scoped applications, and all integration touchpoints. Without this baseline, preparation is guesswork.
Run the Upgrade Preview against the target release early
The ServiceNow Upgrade Preview tool shows you exactly which of your customizations conflict with the incoming release. For heavily customized instances, the output can be substantial. Running this early — ideally several months before your planned upgrade — gives you time to work through remediation without time pressure.
Classify and prioritize skipped changes by risk
Not all skipped changes carry equal risk. A skipped change to a UI policy in a low-traffic module is very different from a skipped change to a core workflow or business rule that runs on every incident creation. Triage your skipped changes by frequency of use, criticality of the affected process, and complexity of the customization. Prioritize accordingly.
Test integrations explicitly — do not assume they will work
Custom integrations are one of the most common sources of post-upgrade issues in heavily customized instances. APIs change, table structures shift, and field-level changes can silently break data flows. Every integration should be explicitly tested against the upgraded environment — not just assumed to be working because it was not in the skipped changes list.
Allocate more remediation time than you think you need
Customized instances consistently require more remediation effort than initial assessments suggest. Complex business rules, multi-layered workflows, and interdependencies between customizations create remediation chains where fixing one item reveals others. Build contingency into your timeline.
Consider a phased approach for the most complex instances
For instances with years of accumulated customizations, attempting a single large upgrade can be high-risk. A phased approach — upgrading to an intermediate release first, stabilizing, then upgrading again — can reduce per-upgrade risk significantly and make each step more manageable.