Mk 2 Octavia - door strap replacement

Help! I need to replace the (worn out, ineffective) door strap on the driver's door, so:

1. I bought replacement part.

2. I then realised that removing/replacing the door strap needs access from 'inside' the door (is this conclusion correct?).

3. I removed the door panel (breaking only one trim clip, and the warning light at the bottom of the panel, in the process).

4. Found that there is a second (metal) panel, riveted in place, blocking and sealing off access to the cavity where the main body of the door strap sits.

5. There is no '5' yet - what do I need to do next to get this 'simple, straightforward job' finished off? 🤣

Do I need to drill out the rivets (but the window mechanism/motor is bolted to that, so the job suddenly starts getting more complex - and I would also need to start buying and fitting riv-nuts to reattach it)?

Maybe I could just carefully cut out an 'inspection/access hatch' in the metal liner over where the door strap is located - having replaced the strap I could then just put a plate over the hole and either rivet it into place (I have plain rivets and riveting tool in the toolbox), or fasten it with self-tappers.

Are there any other options you can recommend? Is there a 'proper' way to do this 'simple' maintenance job, or is it always going to inevitably be a bit of a dogs breakfast?

Any thoughts?

Thanks all. Stom.