Edit template prior to sending for signing

Hi All, I am trying to create a template that can be used by the team to send for signing. Creating the template is easy enough however my challenge is how to create a template that allows for one of my team to insert some data in predefined fields and then send for signature.
There are 3 fields that I need to be able to be edited by one of my team, but locked and non-editable once it is sent for signing.
I know I can just enter the data into the template, save and then send for signing however it being able to do it all in one workflow would be preferable.

I would appreciate any help.

Cheers