Could they? At least for stratospheric aerosol injection it would be easy to just stop doing it if things seemed like they were tipping. It doesn't happen _that_ fast, we'd have time to notice and react.
I'd say that things are not bad enough for anyone with the means to take the risk. When the things get bad enough for the Overton window to admit geoengineering, it may be too late for simple and affordable solutions, as usual.
(It would be ironic if the world's response to fossil CO2 emission is to mandate extra high sulfur jet fuel, but nothing would surprise me)