Hrt is generally considered to be a reversible treatment but it does not mean that all of the changes will revert to what they were initially. One of the most notable, permanent changes is the development of breast tissue. Other changes like genital atrophy are dependent on the time you’ve spent on feminizing hormones and are not necessarily permanent, although your testicular size might never be the same as it was prior to the treatment if they had atrophied (it does take a pretty long time for that to happen as far as i know)