Hmm, not sure I understand your question. If you mean "lighten" the trigger pull, I've never heard about a screw adjustment for Sig's. If you mean shorten the length from the backstrap to the front of the trigger (very useful for smaller hands), this can be done by changing the trigger. Sig, and some aftermarket vendors, makes a short trigger for the P228/229 that does this. I installed one on my P228 because I have small hands with short fingers. It made it much easier for me to grip the gun and squeeze the trigger properly.
Regards - AZFred