Can I change the number of hops Tor uses?

Right now the path length is hard-coded at three (except if you're accessing an onion service).

Why not longer?

We don't want to encourage people to use paths longer than this as it increases load on the network without (as far as we can tell) providing any more security.

Also, using paths longer than three could harm anonymity, first because it makes denial of security attacks easier, and second because it could act as an identifier if only a small number of users have the same path length as you.

Why not shorter?

If we made two-hop paths, then a relay on either end of the circuit would know which relay it needs to attack (whether break into, collaborate with, or maybe just surveil) in order to identify the user.

Whereas with three-hop paths, a relay on one end doesn't immediately know which relay they would need to attack, increasing the cost, effort, and uncertainty of an attack.