PIC's do tend to remain pin compatible, that's one of their excellent features. However, I would expect you would need to alter the config lines considerably.
Even more of a concern though is the banking, it's done completely differently in the enhanced series (using a bank register) and has a HUGE number of banks. If anything it's actually easier, and if you used the Banksel macro, it will automatically insert the correct lines - but because of the much larger number of banks you need to switch banks a LOT more than the old series (but it's a fast single line instruction now).