my AOS was approved after my interview two days ago (family based/unmarried son of u.s. citizen), I was not ordered a gc because at the time I was affected by the retrogression. however, my PD will be current again in november.

I have a SS card that has always had a printed restriction. rather than getting in removed after receiving my EAD I chose to wait and make one trip after my CG is in hand. my question is: am I eligible to apply for an entirely different SSN as a GC holder? or do I have to stick with the one that was originally assigned to me many years ago.

I've spent my entire life entering "non-resident/citizen" on applications that also required my SSN and I fear that my number will forever be associated as to one belonging to an alien. I'd like to have a fresh one, if possible, that has never had any restrictions placed on it.

That is your SSN to the grave and beyond and unless you submit proof of U.S. citizenship your SSN record will always have the CSP code of B, even if you were assigned another SSN.

https://s044a90.ssa.gov/apps10/poms.nsf/lnx/0100209004
RM 00209.004 Basic Format for Numident Query Responses

CSP: Citizenship Code. (A=U.S. Citizen; B=Alien allowed to work; C=Alien not allowed to work; D=Other: Alien not fitting category B. or C.)