Dism , probably not a good idea to mix a 400 with a 460. reasons...
1 - The ferrule may not be exactly in the middle therefore it may not be the length you expect
2 - Its gonna mess up ur IMCS number just because a 400 is about 19 and a 460 is 25 doesnt mean ur makeshift 430 is gonna be the required 21. could be too soft at the bottom or too hard and ur sail probably wont set right.
Mabbot , The ferrules on masts are NOT a generic size.
sometimes they're even different between alternative models of the same brand.
EZZY masts that you can buy each half individually are the only one that i know of that u can mix and match and i think its only for the skinnies.
Its so that if you bust one half, usually the bottom you dont have to go out and buy a whole new mast , just the half you broke - good idea really.
Correct me if im wrong and i hope that this helps - sorry for the bad news but it looks like ur gonna have to buy a new mast