How can I have a custom form be selected when a record is created based on a field value from the referring record? I tried using a workflow but it was not working.

I'm guessing you'd have to script this for reliability purposes - workflow should in theory be able to handle it, but data off of a related record might be challenging

@KevinJ of Kansas Yup. Thinking that will be the way to go. I am a bit new on scripting so this would be a good way to get my feet wet. Did try worklflow using Entry as the trigger but the form did not change.

before record load or after field sourcing is probably what I'd pick - and I'd expect there to be challenges either way

you might have better luck setting the custom form from whatever is creating your second record