I do not think smearing an abrasive paste inside your BB is the best idea.

If rust is your issue in there, either linseed oil painted in with a brush after a light
wire brushing to get out the big chunks, or even a light film of grease as you
regrease the bearings ought to work.

You might want to consider replacing your spindle and BB bearings with
a sealed unit if it's a continuing problem.

Regardless, fine abrasives and bearings are a bad mixture.