Once working credentials are discovered for a device, they will not be changed until they are found to no longer work. After they fail, "re-guessing" will commence which will follow your modified global list of CLI credentials to try.
Back in 2016, Marc Jensen explained two ways to do this faster or more efficiently. I've used method (2) before successfully.
1 - You can force NetMRI to re-guess CLI credentials by issuing the "reset cli" command in the admin shell. That will reset the credentials for all devices, not just the ones in a particular group -- but it would be a quick way to ensure that re-guessing takes place.
2 - If you know which devices had their credentials changed, there is a way to bulk-import the correct credentials for those devices. This would be the equivalent of going into Device Viewer for each device and entering the correct credentials for that device, but accomplished in one step by importing a text file. Detailed instructions and a description of the file format are in this KB Article - https://support.infoblox.com/app/answers/detail/a_id/3636
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