The sailor is responsible for his rating.... If the RC made a mistake... you don't get to keep the trophy.... you are supposed to report it.... and correct the scoresheet.
Doesn't matter if its portsmouth, PHRF SCHRS etc. etc.
So, you make changes to your boat... you are responsible for correcting the rating if its warranted. You have to know your proper rating for the modifications you made.
In the case noted above we have many once a year racers show up... I am not about to tell them no you can't race after they drove 100 plus miles, paid for a hotel, and an entry fee..
With DP-N we can fix that right then and there with the published modifiers... I am not saying they are fair or accurate, but....... With SCHRS, not such an easy remedy... Joe Blow sailor may not have an interest getting all the "T's" crossed and "I's" dotted with being SCHRS compliant. I have directed a few people to the web site and told them to get the measurements form their sail makers so we can come up with a number..
Put yourself in my position.. how would you handle this situation.... a.) Tell them tough luck rules or rules you can't race b.) tell them those are non stock sails and there is a 5% penalty until you can provide a measurement. c.) Stick with DP-N.