Best Practice for "Customizing" Form and Approval Builder and Fluid Approvals

TLDR: what is the best practice approach for modifying objects created by Form and Approval Builder and Fluid approvals "beyond" adding a "known" field?

Using PeopleTools 8.58, HR and FS 92 (PUM through January)

In some cases requirement is to add a behavior (a la event mapping) or object that isn't in the delivered component (e.g., set of rows). However, Form and Approval Builder and Page Composer (for Fluid Approvals) generate generic objects that are shared by other transactions.

What's the best way to "customize" as above? If we modify the delivered "core" generic component or apply event mapping to the core component it doesn't "know" which transaction it's really trying to modify.