If you're not opposed to cheating, with testingcheats enabled (press Ctrl Shift C) to open cheat window), shift-click the Sim and chose Reset from the menu. This will usually work even if you can't cancel out the Investigate Strange Light interaction. You have to catch them before they start rising, I think, tho.
MC Control Center Mod (MCCC) has an Occult Settings Module, in which you can change the frequency or turn off Abductions. It is a large mod with a lot of functions, including story mode features. You have to turn everything on, tho, so even if you just use it for just this particular thing, it won't do anything else. All MCCC Settings are at Default (Game) options until you change them, and quite often Restart. It is found on Deaderpool's MCCC site, and needs updates with Game Patches, usually, as most script mods do. Script Mods must be enabled in TS4 Game Settings, as well.
