You can reactive a Pro subscription for a paper, depending on how you cancelled the Pro account.
If you have cancelled your Pro plan by deleting your paper:
Unfortunately, you can not reactivate the subscription since the paper and the Pro account no longer exists.
If you have cancelled your Pro plan by clicking "cancel" in your Account settings and your paper still exists :
Contact us to reinstate the subscription.
You can also wait until the end of the billing cycle for your paper to downgrade. Once your paper has reverted to a basic paper, you can then upgrade by clicking the button found on on your Paper Settings Dashboard.
If you re-upgrade yourself, you will need to enter your payment information again to begin a new billing cycle.
Any customization settings that were added for your Pro paper will remain saved as long as you don't over-ride the setting by making changes when your paper is a basic paper.