Promote user from a template to another

[fralolo]

I'd like to be able to "promote" a client and/or a domain from a template to another.

For example, imagine I have a client created with the template "mid-sized client". But the client grows and grows and he looks like more a "big-size client"-template client than the "mid-sized client"-template it is.

Currently I would have to
A) Delete the client and re-create again with another template
or
B) Upgrade manually the limits for the client

WOULD BE THAT DIFFICULT TO DO THIS AUTOMATICALLY??????