First, Scotus changed uniform issues.
Second, retired receving pay are rotc instructors, service school instructors, and the like.
I guess admitting you are wrong is difficult.
SCOTUS may have changed uniform issues RE the Stolen Valor Act, they did NOT change the uniform issue RE U.S. servicemembers or retirees.
Here is an article by Staff Judge Advocate officers discussing retirees and the UCMJ (I'll save you the trouble - yes, it is applicable):
https://www.jagcnet.army.mil/DOCLIBS/MILITARYLAWREVIEW.NSF/20a66345129fe3d885256e5b00571830/47c2b664085060fc85256e5b00576e6e/$FILE/Volume175Davidson.pdf
Further more, Article 2 of the UCMJ does not make the distinction that the retirees have to be ROTC instructors or the like....only that they are receiving pay (e.g. a retirement check).
If they are not on active duty, and are ROTC/school house instructors, they would be either government civilians or DoD contractors....and STILL prohibited from using a military uniform to bash a political candidate.
This is another article discussing the similar though it says while retirees are subject to the UCMJ, they likely will not be prosecuted by a Courts Martial for smoking pot.
http://www.military.com/daily-news/2014/07/14/retirees-unlikely-to-face-ucmj-charges-over-legal-pot.html
Here it is spelled out in plain English:
http://www.military.com/benefits/military-legal-matters/military-law-overview.html
Generally the military will not recall a retiree to active duty for a courts martial unless #1 the retiree committed a crime on active duty that wasn't discovered until after separation (for example espionage), or #2 the retiree commits an act that brings discredit against the service........
If some USAF brass decide the officer in question brought embarrassment and discredit to the USAF, (particularly from using their uniform and rank to bash a political candidate) they most certainly could conduct inquiry, recall the retiree, and subject the retiree to Courts Martial; suspending retiree pay and placing them in active duty pay status until the results of the trial - e.g. not guilty, or some punitive measure (which could include forfeiture of all pay and allowance.
You are entitled to your own opinion, you are not entitled to your own facts.
The UCMJ is clear - it applies to retirees receiving a retirement check.