How to replace XG2 with XG1v4?

Your only hope is to try and contact Comcast. XG1v4's are still in very short supply, despite massive cord cutting and people cancelling service. It's remotely possible a local Xfinity Store may have one, but don't count on it.

Hello @user_02338f, thank you for reaching out to us on our community forums! Could you please send our team a direct message with your full name and full address? Our team can most definitely take a further look at replacing your box with an XG1v4.

To send a "Direct Message" to Xfinity Support:
Click "Sign In" if necessary
Click the "Direct Messaging" icon or  https://forums.xfinity.com/direct-messaging
Click the "New message" (pencil and paper) icon
The "To:" line prompts you to "Type the name of a person". Instead, type "Xfinity Support" there
 - As you are typing a drop-down list appears. Select "Xfinity Support" from that list
 - An "Xfinity Support" graphic replaces the "To:" line
Type your message in the text area near the bottom of the window
Press Enter to send it
 
See https://comca.st/3KQF8q9 for an example.