Is there a trick for removing the pins of a female JST-XH (2.5mm) connector from the plastic housing?  The fan cable on my Fat Shark battery has failed (a common problem, apparently) and I need to splice in some new wire.  I can see the springy retention tabs on the pins, but haven't had any luck pulling the pins out even when I push the tabs down flat with a sharp tool.

No, that is all you need to do. You're not pushing the tabs down hard enough. Sometimes you need to actually push the tab down into the cutout of the pin itself to ensure it is below the flush line, and then bend it back up out of the cutout again before refitting the pin.

If you still end up struggling, use a pointed implement like a dressmakers pin and press it down into the top of the tab while also pushing it forward to try and force the pin out from the front. The point on the pin will dig in and get a purchase on the metal to help push it out.

OK--thanks, Snow! I'll try harder . . .