Where rules apply to a specific model, they always override any contradicting basic rules. For example, the basic rules state that a model must take Panic test under certain situations.
If, however, that model has a rule that makes it immune to Panic, then it does not test for Panic – the advanced rule takes precedence.
On rare occasions, a conflict will arise between a rule in this rulebook, and one printed in a Warhammer army book. Where this occurs, the rule printed in the Warhammer army book always takes precedence.