78/79 Modifiers

Can/should 78/79 modifiers be used with an add-on code?

Example:

Pt had a kidney transplant 09/20/15 (50360 & 50323-51/RT).

Pt then had an incisional hernia repair with mesh on 10/21/2015 which was coded as by our coders:

49561-78
49568

We are not sure if the add-on code needs a modifier due to the previous major surgery.