I guess I have 2 questions:
1. Can an Opportunity (created as an Opportunity) be changed to a Lead?
2. Can an Opportunity, that was converted from a Lead, be reverted back to a unconverted Lead?
With the stock functionality, I don't see a way to achieve this, however doing this with a customization should be pretty straight forward. I could see this working with a special button added to the recordview, see something like this:
Or also with a logic hook where you could add a field "reconvert" and in a before_save logic hook check that field, create a new Lead and copy the values over where applicable / check for the original lead and change the status / delete the opportunity using normal Bean Factory.
Is that something that would help for your use case?
Ah I didn't really touch the first part of the question, I think changing an Opportunity to a Lead is not really possible, how I would approach it would be to take the data from the Opportunity and copy that over to the Lead.
Retrieving data ...