try the sedcmd command in the props.conf, and deploy on your parsing instances :
see http://docs.splunk.com/Documentation/Splunk/6.1.4/Data/Anonymizedatausingconfigurationfiles
on all indexers
on all heavy forwarders
in case of csv/iis or INDEXED_EXTRACTION sourcetypes (since splunk 6.1), on the forwarders (even the Universal and Lightweight)
[mysourcetype]
SEDCMD-hidessn=s/(GovernmentIDNumber: SSN: \d{3})(\d{6})/\1xxxxxxx/g
GovernmentIDNumber: SSN: 555666666
-> GovernmentIDNumber: SSN: 555xxxxxxx
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