Originally Posted by
NuclearTumbleweed
I recently cleared TSA at JFK T4 with a T2 boarding pass with no issues, so it definitely can be done there. T2 and T4 have an air-side connection through the Jitney shuttle, and you just need to show a boarding pass to get on the shuttle. I personally haven't had any issues with this bus, but I've heard an anecdote of someone only being allowed to take the shuttle to the terminal on the boarding pass, even when explaining that you're trying to get to a T4 lounge. YMMV.
Beyond JFK T2/T4, all the PHL terminals are connected air-side. LGA C/D are connected air-side with moving walkways.
Thanks for this as well. It could be helpful to compile this info for major airports in a list, but I'm sure someone here on FT has detailed it somewhere... It seems like the rule of thumb is that it can't hurt to try and change terminals as needed for lounge access if you have the time and aren't being a burden on security, of course.