> Whilst I love Affinity Designer as a program, the problem comes when clicking Save in Affinity Designer,
> as it wants you to save as an Affinity Designer file first, rather than just making an update in Cartoon Animator.
Affinity Designer (or Photo) works perfectly well in this context. Sounds like you've missed the simple step that's required in the Affinity apps.
Preferences > General > Enable "Save" over imported PSD files > yes please!
