if the model and the rig are under the same group (ie, you selected them all, pushed the up arrow on your keyboard a couple times to make sure you have all the object's existing parent groups, or just select the parent node in the outliner or hypergraph, and then pushed ctrl+g) then resizing the group node will keep everything proportional

you can't 'unfreeze' transformations unless you undo
because to 'freeze' transformations is to reset translation and rotation in the channel box to 0 and scale to 1 with the current model
you can't go back unless you hit undo