Migration without creation new accounts

Hello all. Please advice me in that question.

I want to migrate our old Zimbra 7 system to the new Zimbra and new server. We had many users in our system and significant traffic. First of all I want to create all existed user accounts on the new server. That will be done by script. After that we planning to start our new system and users will be able to login and send-receive mail. After that I want to starting migration process through Zextras Migration Tool, and users will receive their existing mail time by time in their new accounts. In that way Zextras Suite will be able to import messages into already existed accounts (without creating new one). Is this option supported by the Zextras suite?

Thanks.