The HUD building code is a national building code. Although those physical changes may be approved for local taxation and assessment purposes--for financing purposes it is still a manufactured home. If originally constructed in the factory to the HUD building code it can never be an "on frame modular home" not matter how much the local authorities approve it or how much documentation they provide. On frame modular are originally constructed in a factory--once they leave the factory any thing can be done to the home which would need to be approved by any applicable local authority. But a manufactured home doesn't have that leeway--as I stated earlier, once a manufactured home ALWAYS a manufactured home for financing purposes.
So if you have a home that was originally constructed to the HUD code in the factory, it should be reported in every appraisal report as a manufactured home regardless of what the homeowner, lender, local building and zoning departments, assessment agencies, insurance companies, etc, etc, etc say. Even if they have a stack of documents 10 feet high saying it now meets local requirements--the original building code followed in the factory does not change. And if that original building code was HUD it is a manufactured home. The report will need to indicate manufactured home, a 1004C attached if for Fannie Mae or Freddie or if FHA the manufactured home info on page 4 of the VC sheet and a requirement on page 5 of the VC sheet for an inspection by a licensed engineer regarding the foundation. Also any and all local information should be provided--but it still remains a manufactured home!