a) Can the policy for an existing object be changed by updating the user metadata of the object with a different set of tags that cause the object to be associated to a different policy?
b) Is there a way over the REST API to get a list of available policies on the Atmos server, how they are triggered (e.g. metadata tag name(s) and value(s)), and what retention and expiration values they apply to objects they are associated with?
c) Where can I get a copy of the Atmos Administrator's guide (or other documentation) so I can see how these policies are created and what the various options are for them?
A) Yes, as long as you have a selector that triggers ON_UMD_UPDATE. Most customers will have two selectors per policy: one that triggers ON_CREATE and one that triggers ON_UMD_UPDATE.
B) Not through the regular REST API, but there is a System Management API that can query policies and selectors. This API requires subtenant admin credentials though.
C) Yes, all the Atmos documentation is available from support.emc.com. You're probably interested in:
System Administrator's Guide: https://support.emc.com/docu44318_Atmos_Administrator's_Guide.pdf?language=en_US
System Management API Guide: https://support.emc.com/docu44320_Atmos_System_Management_API_Guide.pdf?language=en_US