Technically speaking, you can do whatever you want to traffic passing in/out of your node. In practice I recall reading that there's some degree of monitoring o

Technically speaking, you can do whatever you want to traffic passing in/out of your node. In practice I recall reading that there's some degree of monitoring on the network that attempts to detect and flag misbehaving exit nodes. You could certainly, for example, redirect HTTP traffic through the Internet Watch Foundations child-porn filters, if you had the connections.