Nice material, but I would apply it to living hinges rather than belts. Using spectra line is much better than belts, will last longer, and is a lot cheaper. Printable belts would perish rather quickly… no reinforcing material inside.
I don’t know about pausing the print and inserting strings but it may be possible to laminate the back of the belt with some spectra line and another material. Don’t know how durable the stuff is either. Any deformation of the tooth profile could muck up the works as well…
Would be aweful fiddly trying to laminate a little belt though!