How can I maintain two separate itunes accounts on one single device without erasing either set of data?

Hi,

Depends on what you trying to setup but for purchases, you can roll down at the very end of the iTunes/AppStore pages to logout of your current account and then login into a different one. Then your purchase will be billded to this new account. Everything will sync as you used to but in order to use the purchased content in iTunes or other devices, you will need to authorize them (you can have up to 5 devices authorized for an account).