Restrict access to value in field value list in MDG

Dear all,

I would like to restrict access to a particular value in the value list selection of a particular field in MDG for a particular user group (users, role or organization). What is the easiest way to achieve this (best via configuration) ? Could I use BRF+ for this purpose ? If yes, how ?

Exact requirement in MDG-S 6.1 Vendor UI is as follows: There are two values in the account group value list (one external number account group and one internal number account group). Requestors should only be able to select the internal number account group. Maybe the external number account group could be hidden as well for the requestors user group. In the final step of the WF Approvers are changing the internal account group selection to the external account group selection.