If you know the name of the field trial you should be able to opt-out on the command line provided you use the correct syntax with the --force-fieldtrials optio

If you know the name of the field trial you should be able to opt-out on the command line provided you use the correct syntax with the --force-fieldtrials option. However it was not established whether or not field trials (A-B testing) was even the problem merely that they existed on the chromium processes. Even the stable version of the browser will likely have these options on the command line.