I hear you, but applying DPN corrections to SCHRS doesn't work. We've played this game locally. Get your sail area if that is the change and run the calculator. It is easy because the numbers for almost every boat are readily available online, type those into the excel calculator and update the sail area. I do this for our fleet, maybe you can designate someone for your local fleet?
You guys are either being idealist, argumentative, or you've never met a casual sailor that does one or two regattas a year on a franken boat. There's nothing wrong with taking what the relative % rating hit in Portsmouth for any of the modifiers and applying it to get some sort of roughly approximated SCHRS number so a casual sailor can pay your regatta entry fee and have a good time with everyone else. While we're taking everything so seriously, we're not noticing how utterly unattractive it is to an outsider.