No, what you're proposing is essentially "turning it off and on again."
If you have access to the old email account, you could continue to use it with your Roku. However, if you ever do need to manage the account (set a PIN to restrict purchases, update a credit card if one is on file, etc) you'll need to be able to log in to the Roku account.
Or, you could create a new Roku account using your email address, and tie the Roku device to your account. You'll need to pick out the apps you want, and log in to any service you have (Netflix, Hulu, etc).
But to answer your question directly, turning it off and on won't hurt anything.
By the way, what issue are you having that makes you want to power it down?
DBDukes Roku Community Streaming Expert Note: I am not a Roku employee.
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