If you integrate the newest Subscriptions API, there is a call to Suspend Subscription.

Presumably it can then be Activated once more (you can test this)

By the way, as far as I am aware the newest version of the Subscriptions API and underlying Catalog/Products and newest format Billing Plan/Agreement APIs (which are not the same as previous versions of the same-named API calls) are not supported by any of the current PayPal SDKs -- so to use so if you do integrate this new Subscriptions API, you need your own direct REST API HTTPS calls, to first exchange a clientid:secret for an oauth2 access_token and call each endpoint.