Second, are you the originator of the YT clip? If not, there could well be copyright issues involved.
Third, what are you wanting to do with the clip once imported? Depending on what you intend, the creator of the clip may consider your "changes" a breach of his/her rights and so would be entitled to compensation! I know that sounds Draconian but copyright laws are designed deliberately to prevent "mis-use" of others' intellectual property.
Fourth, and in strict answer to your question, yes it can be done! Though I don't think "directly", i.e. you would need to download the clip first using a tool such as "YouTube Downloader" (basic version free, I think) and then import the resulting file to MEP.