Overall though, I think it will add more time to your charging time though. I'm not certain on that because I don't DC fast charge but I think it will, at times and certain points of the charging curve, prolong your charge and cost you more money if you are paying for the power by time and not electrons.
The AC uses so little power that it won't make too much a difference even when the battery can accept 55 kW. We're talking maybe 2% of the power? That would be something like an extra minute of charging. But especially after the step down curve begins it is a non-issue since the vehicle will draw what the battery needs and then the AC power above that. So if you are paying by the minute you get a better value after the step down by running the AC than if you aren't.
AC draws a few kw max. Mostly 1kw ish once it reaches equilibrium. It won't affect charging time unless the charger has been maxed out, which doesn't happen all the time with a bolt. It will cost more if you are charged by kwh though.
An Ontario mechanic has apparently successfully done so, not sure how involved it is, but the Power Distribution module would need to be replaced. There is probably some programming needed to support it, using the Diagnostics port.