Can transgender people grow mustaches naturally?

I've heard you can stimulate the follicles by shaving which can increase thickness of facial hair. Even if it does become darker it will probably not be the same as a mustache grown through testosterone.

The word 'transgendered' is incorrect, the word is transgender or you can say trans.

Yes, trans men can grow mustaches naturally - as cis women can - due to natural hormonal fluctuations in females, but also of course if they take hormone treatment they can grow facial hair.