[wee2er]

There's nothing stopping you reverting back to PM / whatever, When you look at the typical timelines reported by clinics etc they all say that most changes are generally reversible to some extent, other than breast growth which is permanent.
One thing to consider when going to HRT is that it is the proper stuff so you should see more and thorough feminisation changes, so just make sure it REALLY IS what you need(not a nice to do / or a want). 
Good luck with your regime.