When I convert a lead to a contact, can I make it set a custom field I have automatically? This custom field does not exist in the leads - only in contacts

e.g Bob Smith is a lead, we then qualify him and open dialogue so want him to be in our contacts, so we convert.

Bob Smith will now be in contacts (and have an account) and I want a custom field of "status" to be set to "prospect"

is this possible?