What is the protocol for re-slinging these? Is it something easy to DIY or better to send off somewhere?
You can easily re-sling them with cordelette, as long as you tie a good knot, but if you want to use webbing you'd have to send them in. Bar-tacking is important and technical and very difficult to do at home. I'd suggest just taking the cord approach.
Also tubular webbing is very useful if you tie the ends together with a water knot