we have the CRM link in our zoho mail suite dashboard.  and works perfect on the left column.

I created zoho CRM accounts using a different domain name for a beta phase testing.  We will now use Zoho with our main domain name hence I need to change all user's emails so they can still be linked to our zoho mail suite. 

how can I change my zoho CRM user's username and email?  what is the best way to approach this?

I have 35 users with zoho mail and zoho crm.

Adding a domain name in zoho mail and setting it to default looks doable however, if we change the domain name (or user's email address) it will affect the link to zoho crm.  Staff will also compain that they will see the old domain name as an eyesore.  

again, please advise what is the best way to transition from my old domain to the new domain name on both zoho-mail and zoho crm?