The fabric on my sunroof liner is peeling, I'd like to take it out and re-glue the fabric. Is there a way to remove it without removing the entire headliner?

 

Yes you can remove the sunroof slider (or whatever you'd like to call it) without much difficulty or removal of the headliner.

It requires removal of the sunroof glass, though, and I would recommend a swivel or wobble extension to get at the bolts to remove the sunroof.

Without pictures this may be a little difficult to describe. But I found some threads on this topic with a Google search:
Sunroof Removal

And there's this, which isn't for a B5 A4, but the way the sunroof goes together is nearly identical:
VWVortex.com - DIY: Removing sunroof, fixing shade guides