We have an issue open to allow a bit more control on the caching modes of virtiofsd but I’m not sure that this will necessarily help you given the topic you’re linking to not really conclusively providing a solution.
You can experiment by renaming virtiofsd to virtiofsd,real and then replacing virtiofsd by an executable shell script which passes additional parameters to virtiofsd.real.
Something like:
#!/bin/sh
exec /opt/incus/bin/virtiofsd.real --my-extra-parameter "$@"
That should make it pretty easy to experiment, though you’ll obviously still need to reboot the VM to change those options.