Extending the Sun's Lease...
According to Martin Beech the Sun could be engineered for longer life by altering its chemical profile through star-lifting some of its mass. ETIs might have already done so to other stars, perhaps explaining (some) Blue Stragglers...
Blue stragglers as indicators of extraterrestrial civilisations?
...which would be an awesome indicator of truly gargantuan engineering. If we starlifted half the Sun's mass we'd have about 10 Jupiter masses of 'metals' to play with. Enough to make several star systems around low mass stars.