How do I customise Tor Browser in a Whonix TemplateBased DVM in Qubes-Whonix

For sure. Having Tor Browser not installed by default (early Qubes-Whonix version…), needing to repeat the installation process per VM, different updater procedures, having to run the updater in more than one VM (let alone more than on the host [dom0]) were among the biggest usability hassles that were identified by usability designer @bnvk when he was working with Qubes.

Would be good if Tor Browser had an environment variable to increase the security slider level. Could you please submit a feature request against Tor Project?
If we had that, there could be a qvm-service which I would develop which would then set that environment variable so Tor Browser does no longer need that modification on the (file level / start change setting level).