Usually if it has been opened before, then the old method of using inertia to eject the chassis from the back case over something like a bed works well. If it has been opened often, then there is usually no significant resistance to simply pulling the rear case off.

My preliminary search also turned up nothing, but I think veterans here and elsewhere know what they look like. The idea of using a putty knife may be scoffed at, but I can remember that tool being advised back then as a ... poor man's substitute. I'm not sure you'd want "pry" it open, as you would want to run it along the seams to try to break the bonds. Naturally, it helps if the screws are out first...

If someone is concerned about the difficulty of opening the case due to age or other factors and the attack of the tool upon the plastic, then electrical tape or masking tape can be applied along the edges. Skill, not brute force, is the preferred technique.

Alternatively, we should heed the advisory on the back panel: "To prevent electrical shock, do not remove cover. No user-serviceable parts inside. Refer servicing to qualified service personnel." I'm struggling on the concept of "qualified service personnel", I think we can self-certify ourselves (late April Fools certification test anyone?).