I think cutting roll film down and taping it would be a pain. I also would worry about film flatness and the focus shift because of the different thicknesses.

I have been cutting down the Freestyle 8x10 Astia with no problems. The colors are not to far off. The best trick I can offer is to use a corner rounder to mark the emulsion side. This lets me experiment with color for about $0.15 a sheet plus developing.