Yes you can.
To edit the plan for one customer please follow the instructions below:
1. Click on 'Collections'
2. 'Contacts'
3. Select the Contact you wish to amend.
4. 'Mandates'
5. Select the Mandate.
6. Click on 'Edit' in the middle of the page.
7. Amend the plan.
8. Save when complete
To edit the plan template:
1. Click on 'Collections'
2. Plan Templates
3. Select the plan template
4. Amend the plan
5. Save.