You can enter them in the appropriate main class Matty, then as many 'duplicate' classes as apply...
so say for example you have a long haired cream - then you would enter him in the LH cream class (this is sometimes split for male/female).
If you are a novice - you can enter that duplicate,
If he is young stock (under 16 weeks) that duplicate,
If you want to enter him in grand challenge
some clubs have a 'small hamstery' duplicate I believe etc. etc.
but only only the one appropriate main class.
Does that make sense?