No, hence why they need to keep getting injected. Same as anyone's body needs hormones to be produced througjout their lives, and the natural decrease with age is part of the decrepitude that happens with age.
It's the physical development that was stalled or altered that is permanent.
There's a case of identical twin brothers you can look up in which one decided to tansition at an early age. The differences between them are very noticeable. Now having reached adulthood, if the one who transitioned decided to transition back, the effects would be more limited, the slighter skeletal build and skull, etc, are permanent.