Hello @muackerm ...

If you have Canvas Studio, then this is possible.  How do I replace a video thumbnail in Canvas Studi... - Canvas Community  However, I'm not sure that replacing the thumbnail is possible if you are recording a video by means of the toolset within the RCE (Rich Content Editor).

I hope this helps a bit.  Sing out if you have any other questions about this...thanks!  Take care, stay safe, and be well.