Lets assume we are dealing with a futuristic setting set several thousand years in the future with major galactic empires controlling thousands of systems and producing all sort of things that we can only dream of as easily as we can produce nails. This includes all sorts of Dyson spheres and super advanced FTL space ships.

This of course includes manipulating metals at a level far surpassing our own. Or maybe discovering all sorts of crazy elements or exotic materials and stuff of dreams, or nightmares...

**Let's assume that an ambitious engineer or someone who owns a sun is bored and asks his people if he can use the sun as a weapon.**

What does that even mean? Either by breaking parts of it off and throwing it at something, or making it explode or go supernova. (I guess, ok I'm bad at science.)

It is probably insanely impractical and the resources needed would be too high and will pose a danger to the system and it might have no value.
*But this is a question of could it be done, not should it be done*
This project is a question of the possibility. We are not worried about anything else.

The answer should rely on some sort of scientific or speculative science basis: up-scaling what we have or modifying certain elements or materials or expanding our current knowledge but with a clear connection to actual science.

I don't want complete fiction like: drop two tons of element *contrivium* and enjoy your desired effect.

And if it can't be done then please explain why.