Don't know about the driver, probably a generic buck driver that puts out a set current (probably maximum 350mA)
You will probably have to find a different driver. With that in mind, also remember that since it is running off of 3 AAA's, it will put major stress on the cells drawing high currents from them, and that will cause the voltage to drop. You could directly swap the LEDs (swap out the xr-c for the xp-g) and probably see an increase in light, due to the xp-g's higher efficiency, but it will not be the full potential of the xp-g. BUT it will also run cooler, last longer.
If you still have a working stock unit, try using some AAA eneloops or similar NiMH batteries. Might work better if it's a boost driver. Still might be an improvement if it's a bucking driver
Edit: btw, that "bubble" is the lens of the XR-C. In the XR-_ series of LEDs, the LED chip sits atop its SiC ESD protection diode, and is surrounded by the metal ring. The glass lens sits on top of the metal ring, and the rest is filled in with an optically matching gel. XR-_ LEDs' domes are very fragile. XP-_ LEDs' domes are less fragile, but still more fragile than the encapsulant used in typical 5mm LEDs.
