Change docs can be purged with standard program RSCDOK99.
There is no need to use archiving object CHANGEDOCU in this context because the delivery and all of it's related change docs will be archived together.
Another alternative is to implement a user-exit rule in the archive program to set the delivery as non-archiveible if the number of CDPOS records exceeds a specific amount. I think there are less than 20 deliveries that would cause this memory issue. This way I can prevent the short dump but I would have to simply leave them on the system.
Also, archiving these change docs with the delivery nearly doubles the run time than if I were to purge them first. I'm on the fence right now as to which option I should recommend.
The deliveries in question are over 7 years old.