So that's my misunderstanding. Your subject clearly states "All User Accounts" and has nothing to do with Administrators. 😲
There does not appear to easily display and edit the users list via the mgmt_cli command. You can export the list of users via Object Explorer in SmartConsole to review their expiration dates. If you have that information, it is possible to track down the UIDs of each user (manually) and use the generic-object API to manipulate the expiration date. This is how I handled it in my test environment.
Since this uses the generic-object API, please proceed with caution.
I created a user "usertest" in Smartconsole. Using the show object with a filter for the username as well as a select filter in JQ, I was able to retrieve the UID for the usertest user object.
[mgmt01]# mgmt_cli -s session.id show objects filter usertest -f json details-level full | jq '.objects[]|select(.type=="CpmiUser")|[.name,.uid,.expirationDate]|@csv'
"\"usertest\",\"75bbb024-de6b-46b1-934f-cea899f7a285\",\"01-Jan-2020\""
Once the UID has been found, the adminExpirationBaseData.expirationDate setting can be adjusted to the new date.
(For full details on the object, use "mgmt_cli show generic-object uid <UID> details-level full"
[mgmt01]# mgmt_cli -r true set generic-object uid 75bbb024-de6b-46b1-934f-cea899f7a285 adminExpirationBaseData.expirationDate "01-Jan-2021"
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Time: [13:46:17] 2/12/2019
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"Publish operation" succeeded (100%)
WARNING: If you mess-up the date field on the user, it will not be properly set. Using a numeric date does not appear to work and will leave the expiration missing.
Results
[mgmt01]# mgmt_cli -s session.id show objects filter usertest -f json details-level full | jq '.objects[]|select(.type=="CpmiUser")|[.name,.uid,.expirationDate]|@csv'
"\"usertest\",\"75bbb024-de6b-46b1-934f-cea899f7a285\",\"01-Jan-2021\""
Keep in mind that use of the generic-object API is not recommended as it's quite possible to quickly mess things up.