From Lead to Contact, back to Lead...

From Lead to Contact, back to Lead...

I'm currently using the CONVERT button when changing LEADS into CONTACTS. However, there is no CONVERT button available under any other tabs. In the event, a client is on a hiatus from using our services, we want to return them from CONTACT to the LEAD tab. How can I convert a LEAD into a CONTACT and then back to a LEAD. Is there a way to add a CONVERT button onto multiple tabs, for example. 
Basically, I want to be able to move leads and contacts and potentials around regularly from tab to tab. 
However, the information fields vary from tab to tab. Is there a way to make the Leads, Potentials and Contacts all the exact same layout?