yes there is a way. I found it casually, but ketron don't want to tell people is dangerous for overvrite internal.
if you want I can tell you how edit original preset, is simple, but please be carefull because you overvrite it
else normaly you search the preset you want to modify, then press long time the key (f2-f3 ecc) and then you enter in program edit, but edit the preset, . of course then you must sate in slot program, if you have 1 voice too... in audya don't exist user voice. else as told you you can Overwrite the original preset. I do it because some sounds not balanced. (many guitar solo are very high level as example).