For testing, we have a way to disable client-side blacklisting of previews optimizations via flags:

--force-fieldtrials=ClientSidePreviews/Enabled --force-fieldtrial-params=ClientSidePreviews.Enabled:single_opt_out_duration_in_seconds/1/host_indifferent_black_list_duration_in_days/0/per_host_black_list_duration_in_days/0/

This effectively sets the timeouts of all the blacklisting rules to 0
except the timeout for the short duration, which is set to 1


For convenience, a way to override previews opt out behavior should be surfaced in about:flags