Yes, I know I can't link them yet, but I have a nagging worry. My GW1 account is pretty old, and the email address used to create it has been deactivated.
Do you think this will cause any problems?
Is there a way to change the email address without much hassle?
You might have to contact support on that. I'm not 100% sure if it sends an e-mail to the old account or not though. It might just send to your new account asking for verification.
Edit: I can't even change my e-mail through the GW client so I have no idea. Just tells me to contact support or check the forums for support. That might be your best place to check.
Edit Edit: After you link them though, your GW account becomes the same e-mail as your GW2. Just try linking first before trying to change just the GW email?