Can you repair coil zipper without replacing the entire zipper?

Hi [insert tiles demonym here]!

I have an LTT backpack, and the zipper is wearing out. The other zipper already broke, which LTT paid to repair under warranty. This ended up being quite a headache, because the repair shop couldn’t find an equivalent zipper anywhere in the EU for shipping (located in France). I eventually found a company in the UK that did custom orders, but the taxes and shipping to France was expensive. The warranty paid for it, but I won’t be using the warranty for the other zipper repair (it’s already an extremely generous warranty, and the damage should absolutely have been classified as normal wear and tear, so I don’t want to take advantage of it again.

Anyway, the zipper for the laptop pouch is showing the exact same signs of wear. I asked the shop if they could repair this one too, and they said no, because the pouch is too narrow to get their sewing machine into. So I can source a zipper, but I would have to hand sew it into the backpack. I feel like I am capable of this, I just don’t really want to do it. I think their might be a way to reinforce it without replacing the entire zipper. I haven’t been able to find any info online about my theory, so I wanted to see if you all had any insight.

The important part of the post:

This zipper is a plastic coil zipper from YKK. They have a continuous coil that is sewn into the tape with thread. The top surface of this thread is ruined by the slider when you zip. This thread is starting to abrade. The other zipper abraded fully in a spot, and the coil separated from the tape.

Here is my theory. If I get a very strong and relatively thin thread, I can hand sew through the coil to replace / reinforce the factory thread.

Has anyone done anything like this before? Any tips, or things to watch out for? Will this change or ruin the smoothness of the slider when zipping?