You can't edit any scans configured in the SEPM from the client side.
You would need to disable the scans from the SEPM and create a new scan locally on the client, which can than be edited.
Once the scan starts, users can stop, pause, or snooze the scan if you allow the ability
Click the Advanced tab on the Administrator-Defined Scans page in the AV policy. Under Scan Progress Options you can give them these abilities.