Hello,
This is just a personal preference so take it just as that. Do not use NER and code your BSFN as C business function, they are easier to mantain, copy, modify. If you have to clone some functionality try to understand what the function does and do it in C, if you have to modify some monolithic NER function try to use the plug and play functionality if that does not work for you do it like Bruno said.
And do not take offense of acid responses, just remember that the people here are not doing this job for fun/hobby, they are doing this for a living.
Cheers,
Dan.