Yes, it can be turned on by Concur Support. We choose to only allow that for certain expense types - meals and transport, basically.
The feature is called "Send Back Expense" and it is simply a checkbox that can be added to each expense entry form. The check box can be set to be modifiable by approvers, processors, or both. When reviewing, the approver or processor can check that box and click save for each line item that is a problem. When they are done, they click the Approve button and the expense report splits in two: part of it moves forward and part of it goes back to the user. The part that gets sent back gets title "Addendum to" the original expense peort name.