You can do whatever you want, but topping autos is not recommended by the breeders themselves, and they are in the business of trying to make their customers happy. If it were ok, then the breeders would suggest it as an option.
The problem with autos is their limited time in veg, before flowering commences. Topping cannabis plants usually results in the plants going through a sort of metabolic trauma (wouldn't you if your head was cut off?!) and this metabolic trauma lasts for between 7-14 days, during which time, very little actual growth takes place, as the plant tries to figure out what has just happened to it. So, with a limited growth/veg period of approximately four weeks with auto flowering plants, any topping done will result in the plant not advancing much for 1-2 weeks, meaning the opportunity to grow before flowering is severely limited. One to two weeks of no growth when the whole growth cycle is only four weeks is not a lot of time to grow before flowering commences automatically. If you are interested in enhanced growing techniques, your best option is to grow photo period plants, whereby veg and flowering times are controlled by day length and you are not constrained by plants that will do their own thing, regardless of what you do or what you would like them to do for you. Hope this helps,.....
Organoman.