Outer Limits 4x4 Board

Hi all
I want to rego my little camp trailer before i change it over to 6 stud axles ect. The tyres on it atm are stuffed but i have a couple of good spares but they dont match. My question is does anyone know if the tread patterns have to match for a trailer blue slip or is it ok if they dont match providing they are in good condition , same size , correct ratings ect?
It is a single axle non braked trailer if that helps.
Thanx Matt

Why not get the blue slip done with the six stud axels and make it a
custom Rego so its all legal.

Blue slip cost the same regardless and should cost some where around $50