I tried that once as a lark....gave myself 15-20 lvls of experience on Peragus, lvled myself up to about 8 or 9....and 1st new loading area, which was T3's section, died. Repeatedly. On normal difficulty.
In fact, T3 couldn't get past the droids at all, even when I leveled him up. So yeah, it kind of works...just have to fiddle w/it enough to find the balance between impossible and not.
And if you do it early like I did, you'd probably have to edit in some weapons too, cause there's no way you're going anywhere otherwise.