I originally, mistakenly, said that way too much had to be undone to get into the box.  All that has to be undone to get to the business section of the circuit board is the metal crimp tabs that hold the top cover on.  The screws and snap clips hold the board onto the base plate, and these do not have to be removed to gain access to the top of the board (and the PROM).  

If you're going in, be sensitive to the need to suppress static charge:

bulletStrive for a static-free work environment
bulletPreferably not on carpet
bulletA concrete floor or driveway is good
bulletNear a water pipe or some other source of ground
bulletNot necessary if working on concrete
bulletDon't be walking around scuffing your feet and building up a charge
bulletTouch electrical ground before handling the circuit board
bulletAs much as possible, handle the board by its edges

 

bulletUndo the crimp tabs
bulletRemove the cover
bulletEt VOILA! (or, as we Tennesseeans say, "Hey ya'll, lookit here!")

Reassembly

bulletMake sure everything is right with the board
bulletNo bent PROM pins
bulletPROM retaining clip installed
bulletRe-install the cover onto the front plate/connector assembly
bulletA bit of silicone spray or dielectric grease on the rubber seal is a good idea, and makes assembly easier
bulletFold the crimp tabs over
bulletIt's ready to re-install