If it's double sided adhesive, warm it up with a blow dryer then slide a fishing line or floss in between the lid and adapter. Heat up the rest of the remaining adhesive and peel off as much as you can. Switch to using googone to wipe off the excess residue.
If it is glued on using cyanoacrylate (superglue) then I would open the lid so that you don't have any chances of getting fluid anywhere near ports. With the lid vertical, put drops of acetone in the space in between the lid and adapter so it starts dissolving the polymerized glue, do not try to peel it off without dissolving the glue first.
The aluminum on a MacBook is anodized to be all the same color, this protection will resist most any solvent short of an acid like oven cleaner. Wise to use a q-tip to test a small spot on the bottom lid (cheap to replace) just in case. Good luck!