How much is it permissible for a religious speaker to copy-paste a lecture from a senior scholar on the Majalis of Imam Hussain a.s? There are young speakers in our community who are straight away copy pasting lectures from senior Alims Word to Word. Is it permissible to sit on the mimbar memorizing a lecture from youtube and then delivering it?

Yes it is permissible. When the senior scholar delivers a lecture they are doing it to guide people and so others learn