If someone shows up to race with a slightly modified boat and no SCHRS certificate then the PRO will assign a rating.
A ha.. the rest of the world calls this process PHRF! (just putting the conventional name to what you do)
Chances are your Race Committee PRO can do a pretty good job of guessing a fair rating.... The sailor can enter the race or not with that rating. The bar could host a lively discussion on ratings or the slimy reputation of XXX or whatever)
How good of a job the PRO does as a ratings expert/ sooth sayer is really not the point....PHRFng the rating is not a good or bad thing...Much of the sailing world in the USA uses PHRF quite happily. its simply just not a transparent or unbiased process.
The advantage that SCHRS provides is that for the NEXT EVENT.... the Owner can go get his gear measured, present the certificate with his transparent rating and play the game with a fully measured boat. Discussion about fair/not fair and bias is simply over. (It doesn't mean everyone is happy with the measured rating... but you know where you stand)