I'm a fan of using the least amount of gear to evoke the best possible result. When you spoke of moderation and low dosing, I was surprised to see you then say "tren" in the next part of your message. Tren is anything but minimal or moderate. Its very powerful and mg for mg, much stronger than test. It wouldn't be my first suggestion based off of what you said you are looking for. I would lean more toward anavar, for a quick cycle, of a moderate compound that is on the safer side, but tren can work. I would just use less. Becuase of the short half life, you will want to inject EOD. I would keep your HRT test where it is and then add in 50mg tren EOD. This will be plenty to make some radical changes. If you want to give my anavar idea a try instead, you could probably make some good changes using 40-50mg ED for 6 wks, keeping the test where it is.
If you want to think a little longer term, lets say 10 wks, simply adding 1cc of deca to your existing HRT plan would get you into a much more anabolic state. I would expect to see some muscle growth and strength increase, but nothing off the wall crazy.
No matter what you do, its the time off between that will keep you sensitive to gear. You aren't going ro ruin your androgen receptors. Just go back down to HRT when you are done and let your body clear out and return to normal