Those properties can only be used as filters; you cannot set to them because there is no setter in the source code. They're constant values based on the PKM class type.
If you are looking to clear all trash, you can do it like so (filter for a specific pattern, clear and reapply):
=OriginalTrainerName=Kurt
.OriginalTrainerTrash=$[]00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00
.OriginalTrainerName=Kurt
=IsNicknamed=false
.NicknameTrash=$[]00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00
.IsNicknamed=false