Is it possible to extend the life of a star?

If something crashed into it rearranging its content a bit, could its life be extended?

Yes! This is precisely what we think causes the creation of blue stragglers.

When we look at a cluster of stars, we expect them to all be of roughly the same age. This is usually borne out by observations. Because larger stars evolve faster, the age of a cluster can then be roughly determined by working out the mass of the most massive star still on the main sequence (i.e. still burning hydrogen in the core). We call this the main-sequence turnoff.

But in some clusters, we see and handful of stars that are more massive, but still on the main sequence, even though all the evidence says they should have already evolved into giants and other more-evolved objects. The consensus view is that these stars are at the very least interacting with binary companions, and many are thought to be merger products. i.e. something left over from two stars merging into one. Either two companions in a binary have orbited so close that they've become one star, or two stars have simply collided (which is quite possible in the dense cores of clusters). Depending on what types of star collide, you can basically get a new star where everything is mixed up again, allowing the star to be "born again".