How would you uninstall the beam blocker if you can't take the grill off?
That's why it's a "project"!!
The burlap can be removed. Or you can find the screw heads and unscrew the beam blocker, then remove it from the inside, but it will leave visible "evidence" on the burlap. The burlap needs to be replaced anyway as it is starting to fray on the edges.
I suppose someone really clever could drill out the beam blocker screws from the inside and then it would just fall out loose.
Actually, the baffle is supposed to be removable, but the person who put the burlap on used a bead of glue, so the baffle got stuck by the bead of glue when it was screwed back on. Someone with the right tools (a very thin sharp edge of some kind like a stiff putty knife? or a heat gun? solvent?) could probably break that bead of glue, then the baffle would just unscrew. I never worked at it hard enough or long enough to get the bead of glue to seperate. I ended up buying a new 2x12 cab, so I gave up trying to do anything to this one.
I personally think it would be better to remove the burlap, unscrew the beam blocker, then just make a small wood frame to hold the new grill material, and use velcro in the four corners to hold the frame in place.
Sorry I dont have better answers. I'm a guitar player, not a woodworking expert. That's why this cab needs a better home.
If you're interested in the challenge, shoot me an offer.