I want to install a phase switch on some or all of the 12 preamps in my mixer. They sound decent, they can make drums sound cool, changing cables is no fun, I wish there were more buttons etc. Should I give up now?

What kind of mixer is it. It might be more of a hassle than picking up a better one. Anything can be done.

its a tiny little logex 8 made by sound workshop circa 1981-ish
i paid less than 500. its sounds cool, i promise. also it has oak sides, so that even from across the room its apparent that you are dealing with a serious piece of furniture.

If your tech savy you can instal a double pole-double throw gold contact toggle switch right between the XLR connector and the circuit . Mount the switch somewhere resonably near the input and have twisted pair going to and frow. Make sure that the shields of the new pairs only connect at pin 1 of the XLR. Map out with your ohm meter the action of the switch. Have one throw be the incoming hot and cold as is, and the other throw be crossed jumpers (from throw 1) so that it would be cold- hot.