An HRT patient can do the same cycles that anyone else can and then return to their HRT dosing when the cycle is complete. The only difference is there is no need for PCT when going back on HRT.
"Bulking" or "cutting" doesnt come down to dose, but more so, to your diet. So you can "bulk up" as much as you want. It all comes down to food. I would not suggest that you let yourself get overly fat in the process. It's always best to keep your gains lean. I would use adex on cycle as well as on HRT, at a lower dose. Your Dr will determine how much adex you need through blood work. Adex controls the conversion of test to estrogen. It has nothing to do with helping you maintain gains.
A standard cycle for a newer steroid user would be 500mg test cyp for 10 wks. Adex will probably be between .25mg EOD to .5mg EOD, depending on your response. From there, go back to your HRT.
One issue I see guys have on HRT, that want to run cycles, is when they don't have a Dr that supports the idea. In the early stages of begining an HRT plan, you may need to have lab work done every month, so the Dr can adjust your levels. Then, many dr's will want you to have labs every 3 months. That does not give a large window to allow for cycling. If you Dr is not steroid friendly, he will not be happy if you have lab results showing your test through the roof. The best thing to do is make sure you have a Dr that understands bodybuilding and will help to keep you safe and healthy through your cycles