Many high-tech materials are effectively a consumable - this post may be the equivalent of asking how to sharpen a disposable razor. Given that it sounds like you're not too worried about the boil-in-the-bag effect of cheap jackets - I'd check prices on replacement jackets before blowing too much money on what could be semi-effective short-lived reproofing chemicals. With a replacement jacket you end up with new zips, velcro, stitching etc.