For the benefit of anyone with the same/similar query coming across this later, the process advised by Noel as above appears to have been entirely successful.

Copying-across the *old* bb folder first to the new PC's C: drive (system drive) took barely a couple of minutes, though handily I had already installed the old drive on the new PC as a slave for easy drag-and-drop of other content which similarly made moving the bb folder equally straightforward.

Installing the previous Full BIAB using the Install Manager required no attention once set going, and completed in around 15 mins to include associated bonus PAKs, 49PAK, RealTraks and a couple of other things in the same bundle.

Ditto the 2024 upgrade-with-extras, a couple or so minutes shorter though the times depend on your system anyway.

No problems or reported issues/glitching to redo manually afterward, and I've checked a little by looking at the What-Add-Ons-Do-I-Have panel and everything is there, also by opening a couple of past projects plus one in-progress, and everything that needed to happen happened and nothing that didn't need to!

Noel: A serious thank you, I'm grateful beyond words.