I don't know about the newer ones, but the vintage RATS used a DPDT footswitch, and either didn't have an LED indicator (early versions) or used a "millenium bypass" circuit to activate the LED but still allow true bypass.
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They don't have the footswitch listed, but I know they probably carry one that will work. To disassmeble your RAT: Remove the control knobs, remove the nuts and washers on the control shafts. Remove the nut from the control switch and DC input jack. Here's where my memory gets fuzzy, but I think you need to unscrew the bushings around the input and output jacks. The circuit card with the pots and switch mounted to it should come out easily.