I’ve done a lot of dumb things in my shop, but the dumbest was converting my 14” Rockwell Delta band saw to cut metal.
You need a cutting speed of 50-100 ft/minute for steel and perhaps 200 for Aluminum, so what type of speed reducer are you going to use??
The Ryobi 9” runs at 3,000 fpm just like my Rockwell so you will need at least a 30x reducer. I tried doing this with a variety of pulley/cogs/belts and was totally unsuccessful.
I ended up with a 30:1 worm drive reducer with sprockets and a chain drive between the reducer and the band saw. All of this cost me more than if I had bought a new cheapo metal band saw!
Also, can you find a metal cutting blade that will actually cut steel in the size you need? You may end up having the blades custom cut.
Fixtures to hold the metal are also an issue.
Basically not recommended.