Dromeus,
It is possible to do it in Voice Edit on the keyboard:
1. Load the SA2 Voice into say R1.
2. Push Direct Access followed by R1 voice selector button to get the Voice Set filter. Remove all the ticks in R1.
3. Now load a conveniently placed non SA2 voice to R1. In the case of the Trombone this could be the Cornet, convenient because it's on the same page for swapping back and forth. With the ticks gone the loaded cornet adopts the Voice Set properties of the trombone.
4.Now edit the cornet's Vibrato speed you want to try. (positive for faster, negative for slower).
5. Load the Trombone again. It now adopts the props of the cornet, meaning it gets its original settings back plus the vibrato speed. Check how the vibrato sounds and if not right go back to 3 and try again.
When finished remember to put the ticks back into R1. Be aware they do not return automatically, even after power off!
You can change the settings in the other vibrato properties but I have not found any response, it's just the speed that is controllable using the above.
The only other blanked property that can be changed, that I am aware of is Mono/Poly which has occasionally been useful for me eg. to avoid distortion through inadvertently scuffing 2 notes while using certain insert dsp's with SA2 saxes.
John