That's sorta what I already said.
(and deciding which local custom, practices, etc., to use and not to use).
Arbitrarily? Source, please.
Arbitrarily? Source, please.
Did the orignal poster say "arbitrarily" anywhere in his reply? Or did you just arbitrarily altered someone else's reply?
To use your own quote again "As we have seen the basis of Common Law was custom. The itinerant justices set out by William the Conqueror examined the different local practises of dealing with disputes and crime, filtered our the less practical and reasonable ones , and ended up with a set of laws which were to be applied uniformly throughout the country."
filtered our the less practical and reasonable ones certainly sounds like (and deciding which local custom, practices, etc., to use and not to use).