You can deregister from the High-Perfomance Computing services at any time from the Registry Info page, found below the service blurb on the RegApp Dashboard or via the menu ribbon (Registered Services → RWTH High-Perfomance Computing → Registry Info).
Under the header Deregister: RWTH High-Perfomance Computing, you can find a link saying Deregister. Clicking this link and confirming the action on the next page will deregister you from the HPC services. Your data on the HPC file servers will remain intact. Under the current Lifecycle Policy, this data is removed a year after the associated account was deleted.
You can re-register for your HPC account at any time, at which point you will instantly regain access to your data, provided no more than a year has passed since you deleted your account.