My guess - they'll just gut the benefits to anemic levels for everyone slowly rather than some big easy to point to maneuver like this.
But, I just looked it up again for this comment and that same rule says "No changes to social security" in reconciliation. It is specifically called out as forbidden to touch via reconciliation unlike almost every other program. So, maybe you are right, it will just be ignored because it doesn't seem possible to quietly change.
If this budget hits the PAYGO limits, which is basically guaranteed, that will trigger automatic cuts to Medicare, so they can backdoor cut the program without anybody voting for that.
Voters over 62 make up >25% of the midterm vote.
By 2030 - that number could easily be >30%.