Peter - thank you very much. That's me sorted now.
For the benefit of any other Mac users that might also want to do the same thing, the corresponding path is as follows. (Adjust according to the specific version of CTA3 you have installed: Standard, Pro or Pipeline.)
/Applications/CrazyTalk Animator 3-Pipe.app/Contents/APData/Default/DefProject.ctProject
If you know how to get into that location and are confident you won't muck about with any other configuration files, that's where to go.
Be aware - you run the risk of breaking CTA and having to reinstall it if you're not careful. If you're not confident in your tech abilities, leave this alone!
CrazyTalk Animator 3 Pipeline (always the current production version, unless otherwise stated)
macOS High Sierra (10.13.6)
Signature data last updated 2018-10-06