Anyone knows whether effects that add extra results to dice rolls count as extra dice for the purpose of triggering lightweight frame?

I mean specifically something like TIE Advanced with ATC that only rolls 2 dice (which would not trigger lighweight frame) and then adds a crit result to that roll. Does it mean there are 3 attack dice now or are there still just 2? Or, to put it in more general terms, do the results added to dice come with a die of their own or do they only exist in a non-physical form? For the most trivial example, if I have a ship that rolls 3 green dice and I use an evade token do I now have 4 defence dice or still just 3?

Yes, adding results is the same as adding dice to the pool. And the timing for Lightweight Frame is "after rolling defense dice", so all attack dice mods will have happened. So yes, anything that adds a result to the attack dice would count towards Lightweight Frame's restriction.

To add a die result, place an unused die displaying the result next to the rolled dice. A die added in this way is treated as a normal die for all purposes and can be modified and canceled.

Thanks a lot!