I haven't tested it myself, only took a quick look for it, but I believe you're looking for the cai_personality_cultural_relations_overrides table. In it you'll find dislikes_highelves_internal. Change the -30 in the attitudes_base column to 0 and that might be what you're looking for. Note that this will not change the wary description in the diplomatic screen. It will still say Saphery is suspicious of other HE factions, and any CAI internal settings will not change so they still might not be as easy to deal with as Ellyrian for instance. The -30 from aversion should go to 0 though.
It might also work to just take the dislikes_highelves_internal out entirely. If I have time to check and you have any difficulties I can do some work with it myself.