I've read this article which tells me how to restore a frozen bucket.
http://docs.splunk.com/Documentation/Splunk/6.5.1/Indexer/Restorearchiveddata
When I restore a frozen bucket, can I select which index it will be restored to? How do I do that?
There is a thawed path for each index you have defined, so when you move the frozen bucket into the specific thawed path, it will be for that index
That would be determined by what path you put it in when you thawed it.
/opt/splunk/var/lib/splunk/defaultdb/thaweddb/ would be main
/opt/splunk/var/lib/splunk/cisco/thaweddb/ would be cisco
/opt/splunk/var/lib/splunk/whatever/thaweddb/ would be whatever
At least if I remember right.
There is a thawed path for each index you have defined, so when you move the frozen bucket into the specific thawed path, it will be for that index