Can I change a Job Template after started...eg square baling job becomes a round baling job?

There really isnt an easy way to change over - you could change the template over on an existing job - I tested this once a job was scheduled with hours in it. This example was a baling job Ive changed to cartage and it has retained all of the "baling" tasks even the hours worked so far...and the only tasks I can now add are the cartage tasks on the template.