What pedal are you considering replacing the footswitch in?
Different companies utilize different switches (for instance, Boss is not the same as Fulltone).
Even if you are referring to a standard 3PDT switch, there are different styles - some have solder lugs, while others attach directly to the circuit board.
Any of the reputable parts suppliers (Mammoth, Small Bear, etc.) offer quality 3PDT switches.
Is it worth doing? Perhaps. Is your current switch broken? Do you gig / tour and simply want to perform some preventative maintenance?
If your soldering chops are good, it's generally easy but you can really mess stuff up if you don't know what you are doing.