Here's an example of adding an enum value to the IncidentSourceEnum, notice that you need a MangementPack and the parent enumeration, in this case, I'm using IncidentSourceEnum, but the principle is the same
PS> $mp = Get-SCSMManagementPack anmpforEnum PS> Get-SCSMEnumeration incidentsourceenum$ ordinal name displayname ------- ---- ----------- IncidentSourceEnum Incident Source PS> $parentEnum = Get-SCSMEnumeration incidentsourceenum$ PS> Add-SCSMEnumeration -Parent $parentEnum -ManagementPack $mp ` >> -Name IncidentSourceEnum.AddedEnum ` >> -DisplayName "Additional Incident Source" ` >> -Ordinal 50 PS> get-scsmenumeration incidentsourceenum ordinal name displayname ------- ---- ----------- 20 IncidentSourceEnum.Portal Portal 0 IncidentSourceEnum.Console Console 15 IncidentSourceEnum.Phone Phone 5 IncidentSourceEnum.DCM Configuration Manager (DCM) 50 IncidentSourceEnum.AddedEnum Additional Incident Source IncidentSourceEnum Incident Source 25 IncidentSourceEnum.SCOM Operations Manager 30 IncidentSourceEnum.System System 10 IncidentSourceEnum.Email E-Mail