You can legally add a "License modifying your Copyright" to your own copyrightable works. However, you must make sure you have permission before adding a license to any "work for hire".
If you do not own the copyright to the work...
and you do not have written permission to add a license to the work...
and there is no license attached to the work giving you permission to re-license the work after you have made an adaption
...just cite the the material and link to it.
Or, if you take a small part, evaluate it for "Fair Use" and cite it - before you share it.
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