You should move all those Library Parts into the Embedded Library before saving back to the previous version.
The Embedded Library is part of the ARCHICAD Project File so ARCHICAD can do something with it (like convert it back to an older version) without affecting any other Project File.
Library Parts in a Linked Library is another matter. If ARCHICAD modified those Library Parts, it could potentially mess up things with other Projects that are using the same Linked Libraries.
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