Does any spring, altering the pull weight, trigger job interfere with the Sig warranty? I assume the work has to be done by a Sig Armorer if the firearm is to remain under warranty.
It might, especially if the altered part was deemed by SIG to be causal to the warranty issue.
Robert Bourke "TheSigArmorer" is a Sig Armorer, so you're good there.
For other brave souls, who might do such work, the spare parts we are dealing with are inexpensive. Should warranty work be needed for something that is not easily field fixable, then the gun can be returned to stock before repair.
I've never returned a gun to a manufacturer, I'm 72 and have been shooting since I was a young teen.
I've done action jobs on a dozen P938's, one truly horrible example had a trigger pull of just over 12.5 lbs, my Lyman Digital scale just went into overload as the hammer released (spec for the gun is 7.5 - 8.5 to their QC guy must have a hellofa callous on his trigger finger to miss that one). Correcting the alignment of the sear/hammer engagement surface dropped the pull by 5 lbs!
These parts don't look to be hand fitted, nor are they machined after MIM moulding and heat treating (one of the things that keeps MIM parts costs down). Good quality or no (not trying to start the MIM debate again - I've done that before), anomalies can happen. If you are buying at a gun counter, and a trigger or whatever doesn't feel perfect, try to compare another of the model you're buying if you can.