If you have Sig do it, you do keep your warranty.
If you just want a shorter reset, consider this.
" Short Reset Trigger package – Retrofit your P220, P225, P226, P226X5-AR, P228, P229, P239 and P245 with the new SIG SAUER Short Reset™ (SRT) sear and safety lever parts. The SRT reduces the trigger reset travel by about 60%. The SRT upgrade is perfect for both competition and combat shooters who want to reduce their follow up shot times. Price includes parts and labor. Original parts returned with your firearm. $99.95"
They also have an Action Enhancement Package.
" Action Enhancement Package*–*Our factory gunsmiths hone and polish critical surfaces to lighten and smooth both the double-action and single-action trigger pulls taking your SIG SAUER to the next level without voiding the factory warranty. (Excludes SP2009, SP2340, SP2022, 226X5/X6, Mosquito, 1911-22, P232/230, P238, P250, P290 and DAK models.) $179.95"
http://www.sigsauer.com/CustomShop/SpecialCTU.aspx