When you initially register for AltspaceVR on your GearVR, the account becomes associated with that particular device. If for some reason you need to use a different Samsung device, but want to keep the same identity in AltspaceVR, you can log in to the new device via the Forgot Password link on the website. Enter the email address associated with the account, and follow the directions for resetting your account sent via email.
Once you've created your password, you can sign-in to the account. This will change the association of the account. Your old device will no longer be associated, and if you were to use that device, you would need to sign-in again. Of course this would then disassociate the second device from the account.