The Evolution Surge series of spells allow an Eidolon to gain additional temporary evolution points which can upgrade them in whatever way the points can be legally spent.
The spell is a transmutation spell, which since the main buff spells bulls strength, bears endurance, and so on are, we know that purely transmutation spells can affect a single target.
So would multiple castings of the spell work? Would the actual choices even matter? So using the points to buy Swim and gills compared to two different elemental resistances, compared to getting two swims?