I have a KAP T-rex riser with a flipper rest all hooked up to some ILF limbs. I get REALLY good arrow flight. Problem is, I hate the flipper rest. Most of the time it's fine, but I drop the arrow off of the rest too often.

So, how hard is it going to be to re-tune the bow to shoot off the shelf? Is that even possible?

You can get the felt pads[from Lowes] and build up the shelf to the heigth of the arrowrest now. Or just put a piece of fuzzy velcro on the shelf and lower your nock to the correct heigth. May not be as forgiving as the flipper rest or plunger button. Thanks, Roy

If your shelf is flat, put a bump under the material you decide to use for a rest, and build out your side plate. Might not be as forgiving, but that doesn't mean you can't get good arrow flight.

Bolt and furniture mover on my Titan:

 

Any bow can be shot off the shelf. several older designs had flat arrow shelves and they worked. It is easier to get good arrow flight if you have a radiused shelf or a raised arrow rest to minimize the arrow contact.

Just reset your nock point for the new rest and tune like you would for a new bow.