Okay, I'm new to AR (bought it less than a week ago), and I searched the forums, but didn't see this question asked before. Is there any way to rename stencils? I have a great collection of texture masks from a 3D program I have, but the filenames are fairly hideous. When I import them, AR just uses the filename.
Hang on, playing around with it, I think I found the answer, in case anybody else was wondering. It also answers the subsequent question of how to delete stencils I no longer care about. In the upper left of the stencil picker, drop down the little menu under the arrow. At the bottom of the dropdown menu is "Manage Stencils." This is a little bit deceptive, because it isn't a stencil manager per se, it's just a generic file manager that is pointed to the storage area for the stencils. Inside you'll find a folder for each stencil subtype to which you have added new stencils. Inside that folder, you'll find the actual image files for the stencils. You can rename these, making sure that you keep the file extension the same (Mac users can ignore that warning).
That's basically it. Just close the file manager window, close and re-open the stencil picker window, and the new names will show up. Ditto if you deleted any stencils (i.e. they won't disappear from your list until you close and re-open the stencil picker). If you have one of the super-deluxe versions of AR, you probably won't want to delete any of the extra stencils that came with it, unless you know you have a copy of them (like on the install disk?).