Sure, you could create a form with a text field, this value could be tokenised and passed into another search further down the page that uses outputlookup or one of the other output commands to save it to a file.
Otherwise you could create your own search command that handles all this for you, here are some links for reading;
http://docs.splunk.com/Documentation/Splunk/5.0/SearchReference/outputlookup
http://docs.splunk.com/Documentation/Splunk/5.0/Search/Writeasearchcommand
http://splunk-base.splunk.com/apps/64805/splunk-dashboard-examples
Finally, if you were really brave you could write your own module that handles this 🙂
dev.splunk.com
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