NO that will ruin the gauge. I just spent some time comparing the schematics for a 95 SPX and a 95XP. There were no provisions in the VTS module on an SPX for a trim gauge.
While I won't go far out on a limb and say you cannot swap a VTS module from an XP into your SPX. I will say in my opinion it is way too much work and way too complicated for a novice. The cost / benefit ratio and the potential for disaster is way too high.
I have a 95 XP and to be candid I rarely look at the trim gauge as I have a better "seat of the pants" indication for the trim position at most times. The only time I may check is when I get back on the ski after a break and forget if it is up , down, or somewhere in the middle.
Robert