Can I change my dynamic QR code to static?

Not the printed one — a printed dynamic QR code permanently encodes its redirect URL, so it will always depend on that redirect service. What you can do is generate a new static code with the final destination baked in, and use that on future prints. Any generator (including QRhubly's free one) can do that in seconds.

When would you? If a destination has become truly permanent and you no longer need scan stats, a static replacement removes the subscription dependency for the next print run. The reverse — turning a printed static code dynamic — is equally impossible, which is why the static-or-dynamic choice matters most before you print. Rule of thumb: decide based on whether the destination could ever change during the printed code's lifetime.