TIR3/LIN3s are sealed, and nearly impossible to break into.
On that note, it is possible... but there's a high likelihood of damage to the head. I had a non-functioning old style metal flange TIR3 that I was able to get into last night, but it was extremely difficult. It's sealed all around the border to nearly 1/2 inch deep, bordered by the circuit board. Go too deep, and you damage the circuits. Once inside, the LEDs are the same/similar to the round units on the older TIR6s/LIN6s/Liberty corners. There's a 4 pin plug, similar to the passive Talon plug, to which the LED board attaches to the flasher board. I was able to remove the LED board, and re-solder on the receptacle of the 4 pin plug, the solder had broke. It was PITA, but I was able to get the TIR3 functioning again. It's no longer water proof, but I keep a junky light around as a 12 volt tester, which this would be perfect for, or in a display unit, as there's no damage to the front. Plus, the metal flange covers up most of the nicks/cuts into the plastic I made breaking into it.
As to the new style plastic flange TIR3/LIN3s, I'm not sure I would attempt this on them.