Yes, just find a not too sharp ended screwdriver and go for it, do this at a screw hole as the gasket goes around them on the inside so you won't easily damage it. The case gasket is not glued or anything, just that rubber "stiction" thing that happens over time. Any gouging of the case can be cleaned up with a sharp knife, and in the worst case (as long as you don't slip in too far and damage the innards) the gasket will be damaged and a bit of silicon sealant will be needed on reassembly. I found starting in the bottom left corner got the result, and for any damage this is the best place to have it for aesthetics (and self drain leaking - but if you are that much of a butcher you don't want to tackle this job!). The attached photos give a clue as to what you are up against.
Please note BEFORE you pull the case apart you should remove the nut around the base of the aerial connector. You can do it later (as I did!) but you are much more likely to damage the gizards which by then are well exposed. I found this nut came undone easily enough with a screwdriver pushing at the slots, but you should use a pair of 90 degree circlip pliars for this - I was just too lazy to go and get them from the shed!
This thread is referring to the following thread: viewtopic.php?f=4&t=4701