What are you needing to change about it? Is it the rule that is bound to it or the underlying datatype itself. If the rulle bound then create a new rule and change the bound rule over. If the underlying datatype I usually create a new datatype with the changes and then change all the references over to this starting at the tables and working thru the rest. But if you think it may change again in the future use a standard datatype and inforce your parameters via Constriants and Triggers instead.