I lacquered a tweed case using 'honey' (the shade) tinted urethane. It came out too dark, and a little green. There is info on how to do it, on the web. It's likely not going to look as nice as a factory-lacquered cab (in my opinion). I had problems with the tweed absorbing the urethane differently in different areas (probably because the glue underneath was not totally even. So it looks a little patchy, too.
If you do it, I recommend non-tinted urethane. And since you're applying your own tweed, you can do a test patch on a scrap of tweed first. 5 minutes after beginning on my tweed case, i realized it wasn't going to be what I wanted, but you can't stop once you start. I did three coats to try to even it out. My case looks like a 'nicotine queen' that has been soaked by beer and cigarettes, even though the leather trim is brand new. If I had to do it over again, I would have left the case as-is. I don't care that much to feel bothered about the way it looks now, either. It was fine before I started messing with it. You're doing your own tweed so you'll have more control over the process, than I did.
There is info on the web about how to lacquer a tweed cabinet... search for it. Some people do use lacquer, but lacquer is a little fussier to prepare, I think (and you can't mix lacquer and urethane). But lacquer may give better results than urethane, I don't know.
If I were you, I'd consider tolex or don't lacquer the tweed. It's a lot of work to change the covering, and then it's a bit of a gamble that the tweed is not going to look how you expect, when you're done.
Just my opinion.
