The only consideration is that you will use Microchips MPASM Assembler (if you don't already do so) instead of MeLabs PM. This entails a bit more fiddling with Configuration Fuses (which on most 18F series are quite convoluted) and a possible edit of the respective 18F's .INC file in your \PBP directory. Beyond that, it's Datasheet time... For example Microchip have a habit of sneaking in additional features into the 18F series which may or may not require some small changes in your handling of internal Registers. The progression path for the 16F876 is to go to 18F242 and 18F252 - a reasonably painless transition... but to progress from say 18F242 to a 18F2420 (because you don't want to use an external Resonator) becomes a bit more tricky because internal Register assignments for unrelated things like the ADC have unexpectedly moved... Datasheet!