Nice one Tonnie, always good to hear from you. Hope you are well.

I find that switching to a 3/4 waltz style when the overall style is 4/4 produces a less than sure-footed changeover when moving back to 4/4.
I stick to the same 4/4 style but change the bar length and tempo as you directed. Then I alter the bass by assigning a hold for two beats and a shot for 1 beat in order to get rid of the 4/4 eighth note feel and make it sound like a waltz. Seems to get round this problem BIAB has with 3/4 to 4/4 metre changes.

Regards

Alan