Similar to this question, I'm interested in having my reports export states/provinces with the abbreviation instead of the full name. The accepted answer in that case was to use an Advanced Search rather than a Report -- but in my case there is no advanced search to get the contacts I need and I'm using a custom report, so I need to figure out how to do this in the CiviReport side.
Take a look at the "Contributions by Organization Report".
CRM/Report/Form/Contribute/OrganizationSummary.php and the line:
$rows[$rowNum]['civicrm_address_state_province_id'] = CRM_Core_PseudoConstant::stateProvinceAbbreviation($value, FALSE);