JIC, here's the VB:
Dim updateParentGroupsTrue As Boolean = True
Dim userInfo As UserInfo = BRApi.Security.Admin.GetUser(si, username)
Dim parentGroups As List(Of Guid) = userInfo.ParentGroups.Keys.ToList()
Dim user As User = userInfo.User
Dim groupInfo As GroupInfo = BRApi.Security.Admin.GetGroup(si, groupName)
Dim addedParentGroupGuid As Guid = groupInfo.Group.UniqueID
parentGroups.Add(addedParentGroupGuid)
BRApi.Security.Admin.SaveUser(si, user, updateParentGroupsTrue, parentGroups, False)
'Remove a group
Dim updateParentGroupsTrue As Boolean = True
Dim userInfo As UserInfo = BRApi.Security.Admin.GetUser(si, username)
Dim user As User = userInfo.User
Dim parentGroups As List(Of Guid) = userInfo.ParentGroups.Keys.ToList()
Dim groupInfo As GroupInfo = BRApi.Security.Admin.GetGroup(si, "Development")
Dim parentGroupToDeleteGuid As Guid = groupInfo.Group.UniqueID
If parentGroups.Contains(parentGroupToDeleteGuid) Then
parentGroups.Remove(parentGroupToDeleteGuid)
BRApi.Security.Admin.SaveUser(si, user, updateParentGroupsTrue, parentGroups, False)
End If