no, it's not region free like you think.
you are thinking of using the a game and an update from different regions, like a korean game and a usa update.
sure, it most cases at least, it probably won't work.
we are talking about since the cia is not the same region as the console, it would not be loaded (or something like that), but on gateway it does.
but on the 4.5 cfw (not gw) it does not. but, you can edit the update and make it region free so it will work on 4.5 cfw.
on gw classic mode unsigned cias are simply not loaded, maybe gw will change that