The answer is "no". Youtube uses HSTS, so any browser connected to Youtube in last 365 days will automatically use HTTPS. And once browser decides to uses HTTPS, you as the middle man can't change its decision. Even the target server can't tell it to use HTTP when HSTS is used.
In theory, you could catch HTTP requests to Youtube, direct them to your proxy and filter out HSTS and redirects to HTTPS from answers. But it would only work for new devices that never connected to Youtube before and that won't ever leave your network, because once they do, next time they would require HTTPS. So in practice, it's "no" again.
People who quote full posts should be spanked with ethernet cable. Some exceptions for multi-topic threads may apply. Not intended as incentive for masochists.