Hi OneLateWizard,
With T, your voice will drop. Read: no more alto. There is no sure predictor whether you'll end up a tenor, baritone, or bass, but you'll definitely have to transpose your whole repertoire, or, for musical theatre, learn different roles that call for adequate pitch. The timbre of your voice will also change and sound more masculine.
Also remember you only have one shot at this, you can't go back if you change your mind later. There are some surgeries, but they're imperfect.
Hope that helps,
Amy
