If you wish to retain the original livery, while in OpenIV extract the file mig29agerman.ytd. I typically extract the original .ytd to the same folder as the dlc.rpf and rename it to origmig29agerman.ytd.
When ready to overwrite with the mig29a livery, toggle "Edit mode", top right button, and drag mig29agerman.ytd from the extracted zip file and drop here:
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