How do you handle existing customers/contacts?

How do you handle existing customers/contacts?

Hi, 

We just integrated MA 2.0 with our CRM and we chose to only import our existing customers contacts. 
In MA they are all "Raw leads" by default and we would like to mass update these to a stage called "already customers" but the last default stage "Sales Ready" is not possible to re-name, remove besides disabling it. 

How do we keep our current customers separate from leads? 
current customers can indeed be cross-selling opportunities and their subdsidiaries might be seen as a lead but the actual current customer is not a lead....

What are we missing here?