If you want to, you can read more than one process if you use other filtering criteria than EQUALS.
See options and further discussion in the links in
Emulate NOT EQUALS in XOG Filter
If you want to you can put all processes in one input file for writing
<NikuDataBus xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../xsd/nikuxog_contentPack.xsd">
<Header action="write" externalSource="NIKU" objectType="contentPack" version="8.0"/>
<contentPack update="true">
<Processes>
<Process code="xx"
...
</Process>
<Process code="xx"
...
</Process>
<Process code="xx"
...
</Process>
<Process code="xx"
...
</Process>
<Process code="xx"
...
</Process>
<Process code="xx"
...
</Process>
</Processes>
</contentPack>
</NikuDataBus>
another option is to use third party tools like ITROI Query Bridge which can process multiple input files.