The following command modifies an existing rule called contentrule by changing the matchtype to prefix and enabling the option to ignore case:

Note: Reference the rule by its name.
curl -k "https://bal:1fourall@20.200.25.100/access/modrule?name=contentrule&pattern=pattern&matchtype=prefix&nocase=Y"

Response: 

<?xml version="1.0" encoding="ISO-8859-1"?>
<Response stat="200" code="ok">
<Success><Data><MatchContentRule>
<Name>contentrule</Name>
<Pattern>pattern</Pattern>

<MatchType>prefix</MatchType>

<AddHost>N</AddHost>
<Negate>N</Negate>

<CaseIndependent>Y</CaseIndependent>

<IncludeQuery>N</IncludeQuery>
<Header></Header>
<MustFail>N</MustFail>
</MatchContentRule>
</Data>
</Success>
</Response>