I would take a look at your existing reporting, view/filters etc. On the off chance that someone has a setup where it's matching 'show me these results where the custom form name contains', your renaming may result in errors in those reports. For a custom form, that would be an unusual way to filter but it's certainly possible. Similarly if you have any integrations (Fusion etc.) that might have that kind of matching.
Other than that, I'd do a text search to see if that custom form's name is mentioned anywhere in an instructional capacity. If your Template description for a particular project says 'Attach custom form XYZ to this task' and your Planner suddenly can't find a form by that name, it can get frustrating quickly.
The system itself references mainly by an object's ID rather than the text name, so all objects that have that form attached would simply display the new name.
Katherine
