Why not? It's likely to be fairly heavy when built at that size so you'll need to consider using 24 or 29 mm composites for power. Another issue might be the dowels on the end of the fins hitting first and breaking off the fins. Shortening them a little or designing them to break away could fix that.
Apogee offers a free trial of it's software rocsim that will give you all the answers you need. Ted
First, do you have the original kit? If so, I know why you want to upscale it. If not, get it, build it and then you'll really want to pull it off.
This kit was my first 'hard' kit. I got it as a Christmas gift and after looking at the picture and the parts in the bag, I quietly put it away for a while. I was intimidated. But, some 6 months later I had a weekend to myself and nothing to do, so I thought I'd give it a serious try and I am glad I did.
The kit involves a few techniques that are more than the typical 3FNC builds. There are a few paper transitions, various detail parts and a neat set of gussets on the motor mount. I simply followed the directions and over a few days, had a really great looking rocket. In all honesty, though, I balked at the painting, so it still sits covered in plain white on a shelf where it won't get damaged. I need to do the paint and fly it, though, as it was a great build.
So, as far as BT-80 goes, I don't see why not to try it. The transitions etc can be scaled with free software, the rocket seems like it has a good length to weight to fin ratio by eye, so I be getting it stable should be easy. I agree that a 29mm MMT is not a bad idea. Although there is a 24mm F32 from AT right now that could also work on a heavier rocket.
Lastly, the dowels are probably going to be tough as Ted mentioned. I also like his idea of making them intentionally break away on impact vs just fiberglassing the heck out of it. To do this one right, I think keeping the aft weight in check is better than getting it too heavy back there and then adding nose weight. The other option could be a separation method where you break the rocket into 2 pieces and bring the back down on its own, oversize chute.
Just some thoughts. I'd like to see it done, so I hope others chime in with good ideas.