Question:
Can I block youtube but allow certain videos?
Answer:
Only within YouTube for Schools, which is a service that filters access to information within the YouTube servers directly. YouTube would need to create a similar service for other users, as their servers are hosting the data.
It should be understood that once an http or https connection to a server by the IP resolved using the sub domain is allowed, potential workarounds to access any data that server is hosting can very often found without using a get request that explicitly includes that subfolder. Attempting to lock down data within a server by subfolder can never be truly secure while the server can be accessed in part. Even if it is initially more challenging to find the video, often it is still possible. This would provide a false sense of security.