4-40 is a slightly larger diameter than M3, so I don't think it will work out well. I don't think the M3 screw will have much bite in the 4-40 hole, though the M3 has much coarser and deeper threads than 4-40.
Going from M3 to 4-40 is another story though, I've done that with great success.
If at all possible, try to test it out on a part you don't need. Ideally you could drill a hole in a new piece of raw aluminum, tap the hole to 4-40, then try to tap it again to M3. But you probably don't have a 4-40 tap....
Jon
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