very good you found one, yes, you will have to open the liner at least along the top half in order to get to the switches wiring on the back-side, good news is it's pretty easy to replace, just match the colors & use wire-nuts to splice it in place.
keep in mind that old wiring is sometimes cotton covered & it can be hard to tell the difference between the colors, keep an eye out for the pairs that seem similar, ( dark & dark, lighter & lighter) so if your replacement switch has say two blues & two blacks, just correlate that to say black is darker than blue, so the darker pair of cotton wires will be a match for the black wires & the blue pair for the lighter set of cotton wires, (in this example) hope that kinda helps...