can you wear silicone ear tunnels when scuba diving?

The risk with taking (shiny, dangly) jewellery near marine visual predators (such as barracuda, sharks, etc.) is that these fish may mistake light flashing off the jewellery as light flashing off baitfish scales, potentially triggering an attack response.

But you're talking about inserts into your earlobes, right? So as long as the inserts are a dull/matt colour, and tight enough not to fall out accidentally (where they might be swallowed by a fish that doesn't know any bettter!), you should be fine to keep them in place while you dive.

And if you will also be wearing a hood (how warm is the tank?), then there's no danger even of accidental loss.

I've never heard of such things as you describe. Why not ask about it before you go on your course? Explain why you want/need to wear them and see what they say.