Google tracks your purchase history under the device's @gmail account.
This is the master copy -- the Google Play unlocker asks Google's servers to check if there is an order.
So, you have to take care of Google's side.
If you're unable to use the same account:
- I cannot change the email in your old order. Google doesn't allow this.
- I can cancel / refund the old order, so you can purchase again, under the new one
- or -
- I can create a free replacement license in my own system, independent of Google Play. You'll need to install an .apk from my web site.
Please decide on which you prefer, and email me at kmansoft / gmail.