I could implement this as a general feature in the Sideview Report Builder, in that I could provide a lookup or two, ship them empty, and tell customers how to add entries to them so as to a) map field names to the names they want to appear in the legend, and b) map field names to names they want to appear in headers.
However, I've thought about it and it's far too complicated to try and explain step by step. Sideview Report Builder with its automatic pivoting and drilldown behavior, has a lot of moving parts already. Furthermore, I think the only real way to change the field names in JSChart's legend is to.... literally change the field name, and this would perturb the entire automatic drilldown stuff that the Sideview Report Builder has going on.
(To explain: in Splunk's general UI's, a drilldown always takes you to raw events. In Sideview Report Builder, a drilldown always plugs in the arguments (even if they're NULL/OTHER), but leaves you in the report builder. Whatever you drilldown down on in the x-axis and whatever was in the 'split-by' UI is now added as new searchterms, and you're looking at a "count of events over time" for those drilldown events.)
Of course, if you have a particular report that you're interested in, why not use the Report Builder's "Create dashboard" abilities to create your own dashboard from that report... Then you can edit the search language once it's created and use rename and eval as necessary to turn it into GB and rename the field in the legend, etc...
