Remove their Apex, or other aftermarket trigger, before sending them back? Also, are the pistols returned to your home, or do they have to go through an FFL again? Thanks.

The requirements for sending a pistol from a home to a repair facility and back are detailed in the ATF FAQ.

See the last sentence above.

I plan to put the standard trigger back in. The Apex folks have on their website words that suggest your Apex trigger has some residual value (i.e. store credit) at their shop, which I think you would rather have than letting Sig toss it aside.

Thanks guys, 4mul8r, you are correct. Thanks.

Of course State law may add additional requirements.