Turning a non-resource level schedule into a resource loaded one (P6)

I have taken over a schedule that is not resource loaded. However, management would like to add resources even though job has already started. The job is a EPC project. The constuction side is resoure loaded but not the engineering side. What would be the best solution for this task? Would I need to make a copy of the baseline, export, make the changes to include resources then import back in?