No that's a good question! In the TDM/prequel, the "personality stuff" will be only for newcomers. Existing characters will be able to tag in while retaining their own identity.

Once the event log goes up, the identity/personality change will affect both newcomers and the older characters. For the older characters, it will be a side-effect of entry into the dimension as well a part of the infiltration process, functioning as camouflage. Let us know if that answers your question!