Is it possible for a Half-Elf to trade a racial trait like Elven Immunity for something like Dreamspeaker? I don't see anywhere explicitly in the rules, and Half-Elves count as Elves and Humans for things like feats.
If that works, then would a Half-Elf be able to use the Elven Spirit feat to trade for something like Lightbringer, also trading in Elven Immunities?
Also, is it possible to take a feat like Elven Spirit after 1st level? It does not specify in the feat itself that it must.
I don't think you can take the racial trades in APG from the Elf, because its by elves. Half elves has their own section.
For feats it is quite possible! Halve Elves count for both elves and humans for race effects.