We have recently upped the limit to 50,000 coupons that can be copied when creating a new race with the copy feature. We also now automatically remove expired coupons, which will not count against the 50,000 limit.
If your race has over 50,000 coupons, we suggest that you keep track of them in separate spreadsheets. Then you can copy the race except for the coupons, and import the coupons on a separate step.
If you have a Partner Account, you can also create coupons that can be shared among races, which may be a better way to handle this type of situation if you want to share 45,000 coupons between races.