Not on a BX mower, but I made a discharge chute cover for my commercial walk behind. I used diamond plate and 2 bolts. I generally just keep one bolt mounted so I can pivot the cover up when I want to discharge clippings, or prevent a mulched windrow by pivoting the plate up an inch or so.
I also use Gator mulching blades which work very well worth either an open or closed chute. On my zero turns I use a commercial product made by Advanced Chute Systems. They are pricey, but the ultimate in convenience.