Switching

Switching is the art of magically exchanging physical features between two targets. The only known sub-group of Switching is Cross-Species Switches.

Nature
Switching greatly resembles Transmogrification, but with with the two main differences: firstly, the features of the two targets are switched simultaneously; secondly, the change in one of the pair is dependent on a change in the other.

It is difficult to gauge the relative difficult of switches exactly compared to other types of transfiguration because the exact year in which they are learn is not known. However, Professor McGonagall was impressed when Hermione knew about switches as a First Year student but was disappointed in Neville for not being able to perform even simple switches by Fourth Year. Therefore, students must start learning switches in Second, Third or (early) Fourth Year (most likely third), earlier than almost all the other branches of transfiguration save transmogrification.