Modifiers definitely should not be amended to add on codes.

Does add on codes need a modifier?

“But generally, add-on codes don't need a modifier to bypass a bundling edit as long as they're billed in addition to the primary code.”

Do you use modifier 51 with add on codes?

Modifier 51 is not appended to add-on codes. For example, modifier 51 would not be appended to CPT code 64462 as it is an add-on code and would be used for any additional injection sites per its definition.