The easy way is just create a ruleset.xml in a location you like and insert the text below into it.
<?xml version="1.0"?>
<ruleset name="MyStandard">
<description>This standard changes the line length</description>
<!-- Insert all sniff from PSR2 standard -->
<rule ref="PSR2"/>
<rule ref="Generic.Files.LineLength">
<properties>
<property name="lineLimit" value="100"/>
<property name="absoluteLineLimit" value="120"/>
</properties>
</rule>
</ruleset>
Use the standard by
phpcs --standard=/path/to/ruleset.xml test.php