Interesting post, and well documented. Are you familiar with the PartComponentDefinition.IsContentMember property? It is a ReadOnly Boolean, so it can not be 'set', but can be used to help determine if you have done enough to the part, so that it is no longer understood as being associated with the content center. Also, are you aware of the other PropertySet named "ContentCenter"? When present, I believe it only contains 1 property named "IsCustomPart", with an Integer type value (most likely zero for False, and 1 for True). Its InternalName is "{ABDA74AD-E927-4CE3-AA83-A5F6EFCE3B75}". If that one is present, you may be able to delete that also. You can also look into the Document.DocumentInterests property, which returns a DocumemtInterests object. When an Inventor add-in (ApplicationAddIn) is involved with that document somehow, there will be one of these in the document for that add-in, and you can check that using the DocumentInterests.HasInterest method, where you provide the ClientID / ClassIdString of that add-in to the method, and get a Boolean value in return. If it contains an interest for the 'Content Center' add-in, then you may be able to remove that by using the DocumentInterests.Item property (and the same ClientID String) to get that DocumentInterest object, then use its Delete method. Or, if the Delete method either does not work, or you don't want to go that route, its InterestType property is Read/Write, and can be set to DocumentInterestTypeEnum.kNotInterested value. I haven't tried process this myself yet, because I have not needed to, but you can give it a try if you want and let us know if it helps any. It may simply not be needed. It lets the system know that there may be aspects of the document that are specific to that one add-in, and maybe what version of that add-in was used. Once you have eliminated the part's dependency on the content center and have it fully independently defined, it should no longer be needed though.
Wesley Crihfield

(Not an Autodesk Employee)