Ok Charlie. Thanks again. But it doesn't work me. I'm more than one way. I'm just giving up. It's not so important, and 2024 is at our door so ... we'll see if there's improvement in this department. What I found (in my case):
1. it works exactly as you say only if you don't touch the APT. If you transpose it, for example, and go back to the original RT as you suggested, the original composition (the original riffs) is lost. You have to regenerate. But, if you can't touch the APT, what's the point of going from unfrozen to APT? I don't see the point, really. I'll just stick with the frozen track. But that's not all ...
2. Sometimes, when I go from frozen to APT (without touching anything, no transposing, nothing) the volume of the track is drastically decreased. So much so that even when setting the APT volume to maximum is not loud enough. Very odd.
3. Sometimes, when I go from frozen to APT, the whole track is moved ahead of some significant time (like more than a bar), so that the APT track is completely misaligned with everything else. Very, very odd.
Again, I'm not wasting any more of my time or anybody's time on this. As I said, it's not important. It might be useful that PGM takes notice that the APT transformation seems to be a buggy, buggy feature. At least in my case, in my system, with my songs. Your experience may be different, I don't know. I'll just live with frozen tracks (which seem to work fine) and, if I need to transpose something, I'll just use an external DAW or an audio edit app.
Thank you for all your help, anyway.