I must maintain my Secret clearance as a DoD civilian (due to my job). The fact that I am also retired military does not make me any more trustworthy for TSA purposes.
many active duty military personnel are entrusted with select-fire weapons and explosive devices. The day they retire, they are immediately "untrusted"
Correct. I can no longer explode C-4, but, I would think that retired military who are also DoD civilains might be a little bit trusted by TSA. I think the same vetting process took place for my military Secret and my civilian Secret clearances.