Think of it like this, at freezer temps the PG or VG does not really freeze, it thickens up a lot, and the molecules slow way down, freezing is not like hitting the stop button, more like pause/ super slow motion. It just greatly slows down the eventual degradation process.
Bringing it back up to room temp, and keeping it sealed until it warms does several things. It keeps the container from sucking in some air when you uncap it, because at freezer temp the PG/VG contracts slightly creating a small vacuum, if you uncap it in that state, air will rush in along with the moisture the air has dissolved in it. Then if you recap it right away, pressure will build up inside the bottle, possibly breaking it.
Warming the bottle up lets everything stabilize back to the state it was in when filled and capped. The PG/VG and nic are not going to undergo any drastic changes from this shift in temperatures, as long as you let it stabilize before opening, and re bottling. There will be some oxygen introduced by the pouring of the liquid, but that won't be too huge of a deal in my mind, because it will be going back into the freezer anyways.