This is unsupported and undocumented command .. having said that, you can do a whole bunch of cool stuff with vimsh.
Specifically for role modification, its best that you manually add the roles and then run a query to see what the role names are and you also will get a lot of that by just looking at what changes in the following file: /etc/vmware/hostd/authorization.xml which is used to keep track of this info on an individual ESX host
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William Lam
VMware vExpert 2009
VMware ESX/ESXi scripts and resources at:
Twitter: @lamw
VMware Code Central - Scripts/Sample code for Developers and Administrators
VMware Developer Comuunity

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