AFAIK XmlInstance API will gladly read 0x56ff0001 xattributes too, provided it can locate the external schema...
I am not familiar enough with that API to tell you how to go about replacing your 'external' ECInstances with ECInstances referring to the stored schema.
If you're very careful, you could probably get away with copying the raw XAttribute data and changing the handler ID directly, then deleting the old XAttributes. Might have to go through the native API to do so though.
Sorry I can't be of more assistance...I am not a v8i guy.
I am not familiar enough with that API to tell you how to go about replacing your 'external' ECInstances with ECInstances referring to the stored schema.
If you're very careful, you could probably get away with copying the raw XAttribute data and changing the handler ID directly, then deleting the old XAttributes. Might have to go through the native API to do so though.
Sorry I can't be of more assistance...I am not a v8i guy.