Yes, I've done it. I've tinkered with episode 2, "RALF," and episode 9. Episode 2 is now much more polished but with the original musical bits left intact. Episode 9 had a song replaced because I like being offensive, but this was WAY TOO OFFENSIVE.
Of course, this doesn't solve the problem that now there will be a stylistic and technical gap between 2 and 3. But I swear I'm done rejiggering old episodes. I promise. Really. For sure.*
* not a guarantee, void where prohibited.