How to change an attribute on a deleted object in ADLDS

Get-ADObject can get objects using the IncludeDeletedObjects switch, but I can’t find a corresponding function with set-ADObject. The issue is that for some reason the UPN attribute is being retained when the object is deleted (even though searchFlags is set to not). I need to clear the UPN attribute from the deleted objects; I don’t want to recover them to do it, and I don’t want to purge them. This can be done via LDIFDE, but I would prefer to use powershell. When using set-object and specifying the DN for the object, but the result is that the object cannot be found. Using the same DN (with includedeletedobjects) and get-adobject will get the object, so I know the value is correct (even storing the get object in a variable, and using the variable attributes to ensure correct values, results in object cannot be found).