novatac bezel removal and lens upgrade question

I ordered a new Ti bezel for my 120p, but I am unsure how to remove the existing bezel.

Also, I plan on changing the lens, but I don't know if I should go with th ucl or borafloat lens. I would really like a strong scratch resistant lens, as the light rides loose in my pocket with my emerson commander, keys, and change. Would the light output of the ucl lens vs the borafloat be noticable? Would it be enough to outweigh the additional scratch resistance of the borafloat lens?

I am going to put in a gid o ring as well, I have heard of a "double gid o ring replacement," what does that entail?

I can only address the first part of your question.
I removed the bezel using a trick I read about here on CPF:
Hold the light firmly with 2 of the grooves of the crenellations pushing on the rubber-coated handle of a small pair of needlenose pliers. Twist off. Worked like a charm.

I mounted my clip under the bezel and needed to use a thicker O-ring to keep the lens tight.

I had a tough time doing it as well until I learned another approach on this forum. Get a pair of rubber work boots or shoes with rubber bottoms that have some tread. Push the light (bezel first) into the rubber sole of the shoe. It will grip the bezel. Hold the shoe with pressure against the bezel and then turn the light. It works like a charm!

I've use the bottom of a mouse pad before. Works well.

My bezel was secured with red loctite and only heat and using pliers on the bezel worked. I tried all the other methods but ultimately had to ruin the stock bezel. A sapphire lens would be pretty scratch resistant but there would be a 10% loss of light transmission IIRC.

Interesting. After carrying my Novatac 85T for 3 solid months, the lens is a bit scratched up. Seems to be some sort of maybe AR coating flaking off if I wipe it too hard. Still, I like the impact resistance, and there's no problems with the beam, so I won't worry about it.

I did however want to mount the pocketclip under the bezel ring. I tried the ole' racquetball trick that some watch guys use to remove the screw-back of a watch if you don't have the right wrench, just hold a racquetball right on there and twist. The bezel ring loosened right up.
I mounted the pocketclip in there, screwed down the ring, and pressed the ball back on there and twist as hard as I could to tighten it up. I have some concerns about it loosening on its own because there's not a lot of thread to engage, but the pre-existing gap was just about the thickness of the pocketclip material anyway, and I tightened it up pretty good. I can't get it back off without the ball.

I love the fact that clip is now tight and in one place, more like a part of the light than an afterthought, not sliding back and forth on the light body under the tailcap. Until I get my flat "P" style switch, I've been loosening the cap a turn when I put it in my pocket. I also occasionally slide a bezel-up light onto the brim of a baseball hat for handsfree usage.