ExpressionBuilder "findChildGeoNodesByGeoNodeUniqueID" from your example is declared in /Stores/WebContent/WEB_INF/config/com.ibm.commerce.store/get-data-config.xml as follows:
<expression-builder>
<name>findChildGeoNodesByGeoNodeUniqueID</name>
<data-type-name>GeoNode</data-type-name>
<expression-template>{_wcf.ap=$accessProfile$}/GeoNode[ParentGeoNodeIdentifier[UniqueID='$parentUniqueId$']]</expression-template>
<param>
<name>accessProfile</name>
<value>IBM_Store_All</value>
</param>
<param>
<name>parentUniqueId</name>
<value></value>
</param>
</expression-builder>
According to expression-builder tag docs, if expression-language is not specified inside expression-builder tag - XPath language is used by default. Unfortunately XPath does not support ordering.
I imagine that you can still implement your own ExpressionBuilder class (I haven't done that), implement any kind of sorting inside this new class, and then specify it in get-data-config.xml