The whole book seems to be about promises made, but also about how to wiggle your way out of fulfilling a promise (made faithfully or forcefully), like the darn True Name change... which it makes it not-so-true anymore, does it?

Oh and the literary plot, i.e. the "soul hairball" that the dragons spit out, this will just help Stupid-human-elf-crying-boy defeat Galby... but that does not have to do with the name unless you count Eragon's promise to rid Middle-Earth of Sauron-DarthVader