Modifiers definitely should not be amended to add on codes.

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.

Can modifier 50 be used on add on codes?

The AMA, in their latest CPT update, has stated that the 50 modifier should not be used for add-on codes. That is, any code that is added on to a primary. A good example of this is the second and third level facet joint injections.