How to keep a MS Word installation working after exchanging HDD without license key at hand? I changed the HDD of a Macbook with OS X Yosemite by taking the HDD out of the computer and making a byte-by-byte copy with dd on Linux. Now MS Word refuses to start saying the copy isn't licensed. It seems to calculate a checksum over the license key and hardware serial numbers and fail due to the change of the HDD.

I have both HDDs at hand and could restore the old installation by putting in the old HDD. How can I prepare MS Word (license) to survive the HDD change?
You need to copy 

/Library/Preferences/com.microsoft.office.licensing.plist

from the old machine to the new one.  Make sure you put it into the exact same location.