You can externalize the validation rules defined in the datatypes.xml file as abstract rules.
First, define such rules as abstract rules and then extend this abstract rule in the datatypes.xml file.
<DataTypes>
<DataType Name="Date" PpcSize="12" Size="7" Type="DATE">
<Validation>
<Regex MaxLength="200" JavaPattern="^[a-zA-Z0-9.,!\-/+=_:]*$"
JSPattern="^[a-zA-Z0-9.,!\-/+=_ :]*$"/>
</Validation>
<UIType Size="8" UITableSize="15"/>
</DataType>
</DataTypes>
<ValidationRules>
<Rule id="abstract1" ruleType="Regex" abstract="true" maxLength="100" minLength="0">
<Whitelist>
<RegularExpression ref="ref1"/>
</Whitelist>
</Rule>
</ValidationRules>
<DataTypes>
<DataType Name="Date" PpcSize="12" Size="7" Type="DATE">
<Validation>
<Rule Extends="abstract1" />
</Validation>
<UIType Size="8" UITableSize="15"/>
</DataType>
</DataTypes>