I use kydex holsters, so it's pretty safe to remove the gun and holster together, and try it on with the new pants. Risk is minimal.
In my old job as a prosecutor, I went suit shopping once, carrying a J frame IWB. Tailor noticed, and once he saw my badge, he asked me to unload, and then let him tailor the suit around the gun. He said he had a number of federal LEOs as clients, so he was used to it.