I suppose there is sufficient time for us to achieve type 2 civ status on the Kardashev scale, that means we cannibalise the Sun! Joke aside would such a civilization level be sufficient to revert a white dwarf into a red giant and finally restore back the Sun to its main sequence stage? I know resources is scarce within the solar system but please look beyond the heliosphere and no FTL.
That is one of the uses of star lifting.
But you would not revert a white dwarf, anymore than you unburn coal. You start while it’s still in the main sequence, and you make the fuel last orders of magnitude longer, don’t waste power lighting up empty space, use it all by stirring it up, and don’t throw large quantities away as a red giant.
In the novella Palimpsest, Charles Stross describes creating a “necro-star” to make the same amount of raw material last orders of magnitude longer. Rather than fusion, the material is fed into a black hole at a measured rate.
You could use a white dwarf as source material in that scenario.