Porting from Xilinx to Altera

If this is in vhdl or verilog, I wouldn't try to wrap the altera libraries with xilinx stuff. Just put it under a revision control system like git or hg, check in your initial xilinx commit, and then rip the stuff out if you don't plan on going back to xilinx any time soon. The start in earnest on your new Altera stuff. Take this as a good opportunity to separate your xilinx/altera proprietary stuff in to nice libraries that you can easily include or uninclude in the future rather than mixing and matching your generic code with proprietary code.