You dont need to "re-seal" them. Just add another layer of silicon sealant in the cracks. Fill the edges so theres no gap, or air.. or anything. You can use clear, or black sealant.... which ever you think looks nicer. Also, those dual halos are nice, but look at Denji's dual halo...my opinion, those are nicer. I have gone through at least half a dozen headlights, and I've never had a problem with fogging... when I seal them again. You dont need to mask anything off.. just cram the tip of the tube against the opening gap... and fill it all with silicon all the way around.
The DIY oven technique... that works really well too.. but you have to be quick before the glue dries. Also, if its an older model, the glue may be so dried out that it wont soften with heat (I've seen this happen only once). Its quick and alot less painless then using a heat gun. I've done this mod several times too. I'm suprised to see it online actually. I've been doing it for some time, and never seen anyone else do it too.