I am adding here the official ways to solve this issue and I know they are not optimal, but it makes sense that these solutions are present here.
The first solution and the most complicated one is to create a Google Store Account and go through all the steps to activate it, with it you can upload your extension package and keep it Private, so you can share the link to this package to who will need to install it, this way that message will never show since the extension has been approved by Google team and it's secure.
The second option is to download the Chrome Dev Browser, linked Here, it wont show on the screen that you are downloading the Dev Channel, you have to trust it is happening. This version of the browser works side by side with the official version so you don't have to uninstall or anything, and all settings are separated so it's really like a different browser.
I am using version 64 of it and it solved my problem with the extension.
