Considering it is an auto strain do you believe it...

you should aim for a great side branch development before considering topping autoflowers.Since most of them go into flowering after just 2-3 weeks of veg,you can do any training within that period.But, if a plant is growing below optimal rate,weak and less side branching,then you definitely should avoid stress methods like topping.If your plant has good development,good branching and in week 2-4 and still not completely in flowering,you could consider topping.But again,aim for max growth of side branches before topping as it will remove your main cola,divide it into two colas that would be equal to that single cola.Those side branches will overcome any downsides/loss of yield by topping if one occurs.If branching is weak,topping won't do magic and you'll be losing yields.As first preflowers appeared on your plant,I wouldn't top it.Just leave it the way it grows will be fine.