I have never used the import key, what is written in notepad is what should appear in the registry, no changes.
I would copy the .reg file from your external drive and then DOUBLE CLICK the .reg file to merge.
Note, I would delete that particular key that you did the test in.
If you wish to test "merge", on the mini, go to the registry, chose a key under software for a program that is not running at the time, export it to your desktop, call it test, save and exit. Then delete that key in the registry, Then double click on the .reg called test on your desktop and it will merge with the registry, you can check it by looking back in the registry, and it should be back in the place from where you deleted it.
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for example:
I deleted a key and below is what shows with notepad, then I double clicked on the .reg file and was asked if I want to merge, I said ok and then got a sucessfully merged message.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Google]
[HKEY_LOCAL_MACHINE\SOFTWARE\Google\No Chrome Offer Until]
this is an image of the merge question:
below is image of success:
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and by the way ACMru keys are just a listing of what you have searched for using Search. not a necessary key for the operation of any program
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by using the import button in regedit, I did not get the merge question but I did get the sucessful message.