Weapon stats dosen't change when using item leveler hack

Do I need to modify some other values so that my level 61 emperor SMG dosen't have the same damage as a level 50 emperor?

it will once you reload the game.. at least it did for me, cause i thought the same thing as you, but after restarting it was all updated.

What about if I use the save editor?

Yup, that works.