I just did this with my 6th gen tail lights a couple days ago, to blackhouse the blinker and remove the orange. Definitely use the oven trick, however, be careful.
I did mine at 260 at first, and left it in for about 15 minutes. This turned out to be a little too long, because it ended up warping it a little bit. It wasn't too bad, so luckily I was able to put it back together without it looking awful.
But anyway, just be careful. I reccomend doing 225 degrees for about 8 minutes, then trying it, then putting it back in for 2-3 minutes at a time, until you can get it apart easily. It doesn't take much to melt that glue.
Also, an easy way to get the watertight seal back together is to heat it BACK up, before you close it together again, then just squeeze the hell out of it to make sure it's sealed. You may want to put some silicon glue in there if you see any areas without much glue left.
Hope that helps