There are two modes the xpathreplacement plugin can be used in. By default it ignores namespaces. If you provide configuration for namespaceMappings then the plugin will be namespace aware and use the prefix to namespace mapping you provide to match your xpath expression.
<country>
<state>
<county>
<city>Norfolk</city>
</county>
</state>
</country><plugin>
<groupId>com.stephenduncanjr</groupId>
<artifactId>xpathreplacement-maven-plugin</artifactId>
<executions>
<execution>
<id>execute</id>
<goals>
<goal>process-file</goal>
</goals>
<configuration>
<inputFile>src/main/resources/test.xml</inputFile>
<xpath>/country/state/county/city/text()</xpath>
<value>Chesapeake</value>
</configuration>
</execution>
</executions>
</plugin><country xmlns="http://example.com">
<state>
<county>
<city>Norfolk</city>
</county>
</state>
</country><plugin>
<groupId>com.stephenduncanjr</groupId>
<artifactId>xpathreplacement-maven-plugin</artifactId>
<executions>
<execution>
<id>execute</id>
<goals>
<goal>process-file</goal>
</goals>
<configuration>
<inputFile>src/main/resources/test.xml</inputFile>
<namespaceMappings>
<p>http://example.com</p>
</namespaceMappings>
<xpath>/p:country/p:state/p:county/p:city/text()</xpath>
<value>Chesapeake</value>
</configuration>
</execution>
</executions>
</plugin>