Replacing var with float will easily break this backward compatibility completely. var is not only used for fixed point numbers, but also for storing engine object handles and pointers. Entity skills are vars, too. So replacing alone won't do it.
Float was just a suggestion because var's are used most often for numeric stuff. If you only have integer values - use integer. If you return pointers, return them in the appropriate format or use simply void* (e.g. for sound handles or do typedef void* SOUND_HANDLE or else).
