Suppose you earmark to a paper on a topic X that SI would otherwise probably not write a paper on. Would that cause SI to take money out of research on topics similar to X and into FAI research? There would probably be some sort of (expected) effect in that direction, but I think the size of the effect depends on the details of what causes SI's allocation of resources, and I think the effect would be substantially smaller than would be necessary to make an earmarked donation equivalent to a non-earmarked donation. Still, you're right to bring it up.