Just put the 12 keys in sub folders of the main instrument usertrack folder and you will be given a key choice in the usertrack picker as to what key you want.
Main folder: Accordion, Rhythm Crossover Sw16 075

Sub folder: Accordion, Rhythm Crossover Sw16 075 key A
Accordion, Rhythm Crossover Sw16 075 key A 01.sgu
Accordion, Rhythm Crossover Sw16 075 key A 01.wav
Accordion, Rhythm Crossover Sw16 075 key A 02.sgu
Accordion, Rhythm Crossover Sw16 075 key A 02.wav


Sub folder: Accordion, Rhythm Crossover Sw16 075 key A#
Accordion, Rhythm Crossover Sw16 075 key A# 01.sgu
Accordion, Rhythm Crossover Sw16 075 key A# 01.wav
Accordion, Rhythm Crossover Sw16 075 key A# 02.sgu
Accordion, Rhythm Crossover Sw16 075 key A# 02.wav

Sub folder: Accordion, Rhythm Crossover Sw16 075 key B
Accordion, Rhythm Crossover Sw16 075 key B 01.sgu
Accordion, Rhythm Crossover Sw16 075 key B 01.wav
Accordion, Rhythm Crossover Sw16 075 key B 02.sgu
Accordion, Rhythm Crossover Sw16 075 key B 02.wav

Sub folder: Accordion, Rhythm Crossover Sw16 075 key C
Accordion, Rhythm Crossover Sw16 075 key C 01.sgu
Accordion, Rhythm Crossover Sw16 075 key C 01.wav
Accordion, Rhythm Crossover Sw16 075 key C 02.sgu
Accordion, Rhythm Crossover Sw16 075 key C 02.wav

Sub folder: Accordion, Rhythm Crossover Sw16 075 key C#
Accordion, Rhythm Crossover Sw16 075 key C# 01.sgu
Accordion, Rhythm Crossover Sw16 075 key C# 01.wav
Accordion, Rhythm Crossover Sw16 075 key C# 02.sgu
Accordion, Rhythm Crossover Sw16 075 key C# 02.wav


You will still get overtransposing as this has never been fixed, it may help if you make a few wav sgu for each key to give more variety to choose from.
If you want soloist do the same but set them as a Drums=True in the Options.txt file.
These won't overtranspose as they are set to drums.
There are 12 key soloist usertracks in this forum to download.