well i had no time these last weeks to have some tests on the big new update with the upright and so on... but tonight, i did.

ell : sometimes when doing a song / piece / cubase projet there is THE perfect sound for a mix, so that it is good to find again that exact right same sound, today, in one week or in 10 years if needed. And it is needed.
For example i have, with Pianoteq v4.2.1, the most fabulous and exact piano sound i dreamed for Messiaen,'s Turangalîla Symphony.

And after installing the v4.5.1... i tested the same Turangalîla movements Cubase CPR, and well, my dreamed Messiaen's sound has gone... it's not bad, but different.

Of course, this is very interesting to go further with research, but i think that it could be good to be able to keep all that was made before, + the new.

So, i would like to have, in my VSTplugins :
Pianoteq4.5.dll
Pianoteq4.dll
( well, for example : i think of waiting Pianoteq5 for further and other new composing and have the U4, to have it beside all versions of Pianoteq  ;-)

( i already have too :
Pianoteq.dll in Pianoteq 3 folder
Pianoteq23.dll
Pianoteq.dll in Pianoteq 1 folder
so that it's OK for all my older pieces without doing anything )

So, i would suggest that you could make a new dll reference when changing the main instrument algorythm method for resonances and so on.
( And having different addons names for different versions,
i.e. instead of KIViR.ptq :
KIViR_v3.ptq
KIViR_v4.ptq
KIViR_v5.ptq ....
so that there would be never risk of conflict in the future.)