If we could create a wormhole at an arbitrary position we could prolong the lifetime of a star to nearly infinity. All we need to do is open a small wormhole at the center of the star and put the end out in empty space. A steady flow of helium rich material would stream out preventing the helium from building up to the point where the star begins creating lithium and carbon.
At some point the mass of the star would drop too much and we would then open a wormhole into the core of a gas giant like Jupiter. The other end of the wormhole could be opened at the surface of the star and hydrogen rich material would accumulate at the surface creating a continuous flow of hydrogen from the surface towards the fusion core.
I wonder if any jets in Active Galactic Nuclei are artificial. They could be evidence of advanced species who are extending the lifetime of their star to trillions of years. The composition of those jets might match the stellar core material of an older star.