@khamus, you can cancel. You have 1 traveling letter, so this should not be a limitation for you.
Members with more then 50 completed exchanges have a limit increase from 9 to 10. Its like having 1 cancel in 3 months mentaining the same limit. For more then 1 cancel in 3 months, the limit drops by 1 for each cancel.
If you have a limit of 10 similtaneous exchanges, you can use it to get addresses. You can use those 10 addresses to send letters or to cancel.
Canceling is an exception. Probably for most members this should be enough. I think it's a reasonable feature. Let's give it a try for 2-3 months and if this is a problem for more members, I will reajust this feature.