If you wish to retain the original liverie pack (gray USAF livery, gray Marine, White Coast Guard), while in OpenIV extract the file ch130.ytd. I typically extract the original .ytd to the same folder as the dlc.rpf and rename it to origch130.ytd.
When ready to overwrite with the additional USAF Vietnam era livery, toggle "Edit mode", top right button, and drag ch130.ytd from the extracted zip file and drop here:
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