If this isn't a change for a major release (e.g., 4.0) then the old functions need to be preserved, and the new versions need to be given new names in the C++ file.  Otherwise you break binary compatibility - so you force user to recompile pre-existing queries.  The ECL name can stay the same.

So for example implement a fsSprayFixed_v2 that has the extra parameter, and call that from the old fsSprayFixed function.