Yes, if you want to you could take a leaf pulling right now. If your plant is healthy, this shouldn't hurt it.
However, you will have to uproot the plant to get a pulling, and in general, it isn't a good idea to disturb the plant's roots as it is going into dormancy because there's a chance that it won't grow them back enough to get re-established before going dormant.
However, from my experience repotting (and I've done it at various times throughout the year), if the plant is healthy, it really doesn't affect it much.
I too am tempted to take some pullings this fall and start them in my terrarium now to have them ready to put outside in the springtime, but I think I will wait until mid February just as the plants start coming out of dormancy. Starting them in February will give them a few months of time in the terrarium to get going before putting them outside.