If you are thinking of resoldering the joints of the fuel pump relay, it can be taken apart without any damage, I did this on my car and it fixed a different problem for a certain amount of time, but in your case, I would not say that is it. Hotwire it and see what happens. If you still want to open it, use a flat screwdriver and lift up the plastic, there is even places where you can do that, then just slide it out. nothing to it really.
1985 190E 2.3L - a constant project.