Hi,
I think MPLAB is a nice IDE for PIC. Regarding retargeting, I don’t think its such an easy task. The logical part will work on any controller, but when you refer a particular peripheral like timer, uart etc. there will be lot of issues.
If you are using only GPIO pins, then change their reference words as same as those declared in the PIC’s header file, and it may work. Replace the code for initial settings like clock settings etc. with normal PIC’s code itself.