EXECUTEJS will replace any variable in the script using the usual syntax before actually executing it, so you can type for example
and it will work
Also are you sure the website doesn't give this? It would match the error you're getting in OB.
(Verification Failed!): The signature or body of the extension has been corrupted and the signature does not verify. Chrome and other consumers should refuse to load this CRX.
I don't think that's possible to do right now, because the user agent is specified through a command line argument when the browser is opened. So that would be a thing that I need to implement in the code itself. Please open an issue on github or I will forget.