Resistor mod like I did on OP in the TK61 mod thread is safe if done properly and with care as far as I know. Improving resistance in the springs on the TK61 will not help you gain anything in output since output is not affected by voltage sag.
Technically TK75 is regulated, but if the output is increased by typical resistor mod, the extra increase in output does not seem to be regulated as far as my experience goes. So resistance mods and good batteries seems to help on a resistor modded light.
Ill probably do a fairly detailed mod thread on the TK75 once Im at the "final stage" along with update to the TK61.
On my sample of the TK75, resistor modding did not improve it that much. Oh well, more about that in another thread..
Glad you got the carrier opened up.
:beer: