you can top autos. however, the faster they mature, the less you want to top them. I'd say don't top fast strain, say under 70 days. Longer maturing strains seem to tolerate it better. I'd say toping twice maybe three times is the limit before you do damage to your harvest. But I can't say this is certain, my tests so far have been limited. after seeing what corgy did to Auto Ultimate with crimping, etc, I'd say that is a strain you may be able to top several times. I may test that idea in the future.
I say though that scrogging autos is more productive. Bend it over shortly before flower. Keep defoliation to a minimum. Doing this maximizes the surface area of the canopy and all buds get plenty of light.