Personally, I tend to stick config information that needs to be application-writable into a database rather than a plain file.

In this particular case, though, you don't need to be able to store it anywhere external to the app once it's been moved to mod_perl. mod_perl provides a persistent environment, so you just need to update the address list in memory and the change will stick around for the life of that process. Granted, each new process spawned will need to repeat the "retry, fail, and update address list" for itself when it receives its first request, but a) it's not that big a deal for each process to repeat that if each process then goes on to handle a couple hundred requests using the updated list and b) this provides a mechanism to automatically go back to using the primary/preferred address after the connection recovers/maintenance is complete.