1) Not currently. Open a support ticket with SmartBear to see if there is a patch available to allow Chrome 66 for your older version. However, minor version updates (from 12.31 to 12.50) are typically free so there is no financial reason NOT to upgrade. If there's nothing preventing the upgrade, that's your better path forward.
2) Not up to us... up to SmartBear
3) It's a very niche extension, not something necessarily globally accessible or needed. So putting it on the Google Web Store doesn't really make sense. However, if you feel you have good reason, contact support directly.
In the meantime... to solve your problem, you have two choices
1) Downgrade Chrome
2) Upgrade TC
