Got a CREE now, how to midify light

I have a CREE on a base and I am wondering about modifying either my streamlight TL-2 or my Inova T3.
The streamlight takes 2 batteries so i guess i could just swap one for one, but the inova takes 3 batteries. In that case does it mean the current is regulated? Otherwise it would be putting 10 volts through right? 3.7x3
Is there a way to measure how much power the LED is getting? Just use a multimeter to the contacts maybe? If the inova is regulated then will the regulation be just fine to switch over to a CREE led or would i need to modify that too?
When it comes to swapping bulbs and stuff thats not too hard but when things become regulated and I gotta calculate electrical factors I get lost.
Heck if i wanted to build my own i would be completely lost about power to the LED. Im not sure how to fid out what an LED is rated up to either.

The Inova is regulated but I've yet to see a mod on a 2007 version and the older versions seemed very hard to mod.

There are plenty of inexpensive buck drivers(like this one) that you could use if you plan on modifying.

Since the inova T3 is a regulated light, if i were to throw in a CREE led, would that make it brighter or just run at an extended time, or a bit of both?
Im guessing its brighter right, because the regulator puts out the same electricity and the cree gets more light out of the same electricity?
Its bright enough for me but I want increased run time mostly, especially because it uses 3 batteries.
Unless someone knew how to replace 3 cr123 with rechargables. I thought about using a 17650 with a spacer but dont know how that will work voltage wise...

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