Does anybody know how to change an Enter key response function for Motion and FCP with FxPlug (or alternative)?

I was able to put together an Automator Service that you can install in your Home folder/Library/Services folder. It will remove any newlines from selected text as well as make sure only a single space exists between words (sometimes an extra space will exist before a newline/return is typed so this makes sure only one space replaces the return.)

This service should be available as a service to any app that supports text (not just FCP or Motion).

You can download it here if you're interested:

https://fcpxtemplates.com/downloads > Remove Newlines (there are a lot of other downloads on that page...)

And, you may redistribute it with your generator if you need to (but don't sell it!)

The simplest method involving the least amount of grief is: don't type the return key in your text... period.

In Motion, the Crawl layout method ignores returns, but opens up a supersized can of worms — but play with it — you might be able to work with it (depending on what you need your generator to do.)

This last suggestion involves writing an Automator Service which will be accessible from the Text field in the Text Inspector in Final Cut which can be made to strip out return characters (and even replace them with spaces if necessary, because that will be an issue as well.) In Final Cut, select the text in the Text Inspector Text box and right click. A popup menu will appear and at the bottom of the menu is an option called "Services". When moused over, a list of system services will appear. Custom services as well. [I'm not all that good with Automator, but some here are - maybe someone can hook you up.]