I've found with plastic sheet or rod that it sands easily enough, but is too soft if re-scribing is needed. I've taken to using stretched sprue (you always have a lot left over, anyway) - stretched a little wider than needed, and scraped on two sides down to the size needed (you can even tapper it if required). Softened with Tamiya thin, and with generous use of the cement while pressing into the gap, when dry, you've replaced with the same plastic, and rescribing/polishing is no problem. You can end up with an invisible seam even after polishing.

2 attached images. Click to enlarge.