No need for an A&P. Anyone can work on an Experimental.
Not to be a stick in the mud but:
Your OP limits probably reference this:
§ 21.93 Classification of changes in
type design.
(a) In addition to changes in type design
specified in paragraph (b) of this
section, changes in type design are
classified as minor and major.
A
"minor change’’ is one that has no appreciable
effect on the weight, balance,
structural strength, reliability, operational
characteristics, or other characteristics
affecting the airworthiness
of the product. All other changes are
‘‘major changes’’
I think VGs would qualify as a "major change" to some at the FAA. Our FSDO (Atlanta) was easy to deal with on a prop and slat removal change. I called with our plan. 5 hours flight testing of climbs, descents, stalls, and handling at various load configurations in the typical geographic area. He took down our N Number and that was it. 5 hours later and a logbook entry and we were done. I am not sure if there is a specified amount of time so you might request less.
It is not a big deal unless you can't get the testing done before some planned long trip or passenger carrying.
FWIW
Maxwell