It should be possible to add and remove assignments of roles to users on MAC Address pools via Administration Portal.
The reasons on a functional level are listed in bug 1863051, comment 2 . This RFE tracks adding the related UI, to keep UI consistent to REST API added in bug 1863051.
This bug/RFE is more than a year old and it didn't get enough attention so far, and is now flagged as pending close. Please review if it is still relevant and provide additional details/justification/patches if you believe it should get more attention for the next oVirt release.
There is no request from users for this RFE, if really needed, that can be done vie RESTAPI. Add proper UI support requires a lot of work, closing due to capacity reasons