From my experience, the best tool to remove pips on the waterline is a diamond needle file. The PL plastic is harder than casting resin and using a sanding block tends to remove more material at the bow and stern than midships.
Cool or cured PL Plastic starts to soften at higher temperatures (around 120C) than cast polyurethane (75C) and freshly boiled water may not straighten a bent hull. I use dry heat in a fan-assisted oven but I will try simmering a bent Chinese warship print for about 15 minutes and report back here.