Once I've edited the file will I need to 'recompile' my build or some such?
Yes. If you run 'make -f Makefile' again (or XCode's build process, if you're using a Mac) then it'll rebuild ShipEntity (and, though there shouldn't be any this time, any other files which might need rebuilding because of your changes) and then remake the Oolite executable.
Once I've edited the file will I need to 'recompile' my build or some such?
Yes. If you run 'make -f Makefile' again (or XCode's build process, if you're using a Mac) then it'll rebuild ShipEntity (and, though there shouldn't be any this time, any other files which might need rebuilding because of your changes) and then remake the Oolite executable.