A Slayer of Terramorphous Class Mod is a guaranteed drop (only) from Terramorphous the Invincible. I believe Terramorphous the Invincible can only be at least level 50 and thus drop at least level 50 items. Can one acquire a Slayer of Terramorphous Class Mod at any level below 50 without the use of such tools as Gibbed's Borderlands 2 Save Editor or Cheat Engine, i.e. without modifying game values from outside of the game client?
As the quest is level 50 (You.Will.Die.(Seriously.) and rewards are always tailored towards the Quest-Level I dare to say the answer is no.