You seem to manage your plants really nicely. I think I have ten thumbs when comes to growing plants so for *me* I would let it grow a while where it's at so that it can get more size on it.
How do you intend to propagate it? I tried growing some sphagnum a while back by putting a layer of rinsed peat moss in the bottom of a tray, layering the live sphagnum on top, and keeping the small tray constantly wet. I missed something and the live sphagnum deteriorated and died on me. I later got another hunk of sphagnum and this time I did not use any peat moss. I simply set the sphagnum down in a tray, (mostly) brown/bottom at the bottom and the green growing tips at the top (yeah, I know...how else would you do it, eh?
). But, there was no substrate...no sand, no peat moss, nothing. This tray of moss is growing nicely. I make sure to keep anywhere from 1/2" to an inch or so (depends on rain) in the bottom and I mist it every few days. Sometimes the rain will put several inches in the tray, basically flooding the sphagnum moss. I'll let it sit like that a day or so and pour most of the rainwater out...the moss seems to *love* it's short swimming session!
With the first batch (that died) of sphagnum moss the peat moss seemed to impart a *lot* of tannin to the live sphagnum causing black tips to form on the leaves. I undoubtedly did something wrong with that batch as I've seen where many people do use a layer of peat moss as a substrate. The peat moss that I used, though, was a *really* trashy brand (Greensmix that I bought at Tractor Supply...FWIW) and I'm very suspicious of it causing the first batch of sphagnum to die...and of some problems with other plants. I may try growing some sphagnum on top of some new, Majestic Earth brand, peat moss and see how it does.
But, as to your question...I would let it get bigger before I try to propagate it. It seems to be happy growing there. Try to replicate that growing condition when you move it. Best wishes!