Re: Changing the plastic covers
You've got a plastic cover on a 59 ? I've honestly never seen that before, only the standard nickle, or brass.
Changing a metal cover isn't that hard but it takes a little work. you've got to cut the solder joint, warm the pickup to melt any wax, then just pull the cover off. Putting a new one on is about the same. Not impossible but if you've never soldered you might want to have it done for you.
If your talking about the actual plastic bobbin thats cracked, then theres really no way to swap that without unwinding the pup which I wouldnt attempt.
If its just one coil though it might be a good option to make a hybrid which is always fun