The answer to the question is yes, it is possible to bulk rename folders ABCDEFGH to ABCD_EF_GH using the Renamer program for Mac. To do so, you can select the folders, then click the "Rename" button in the Renamer program. You can then enter the desired pattern (ABCD_EF_GH) into the "Pattern" field and click the "Rename" button to apply the changes.