The trimmed opening is 24.50″ wide by 32.00″ high.
Most kegerators are about 48.50 high with the tower attached, 20″ to 24″ wide and 24″ to 25″ deep. Without the tower they are usually 35″ high.
To shorten the kegerator, you can remove the upper rail (if equipped) and remove the feet or casters to buy more space. If you still need more height, just assemble part #24 of the keg box framing with 4 screws (no glue), then once the bar is ready for final trim, remove part 24 and the bar top supports will keep everything securely together. That will allow for a 38.5 high opening, more than enough for any store bought kegerator.
The depth should be OK. The bar provides a full 24″ (25.50″ to back edge of base), but some kegerators can be slightly more at 24 13/16″. In those cases the door will extend out an inch or so, but that is fine.