Lost a few links from a Shimano 10 spd chain the other night. Can I splice in a few unused links from a 9 spd chain to get it back to the right length?
According to Sheldon, the pitch should be the same, but the width may be slightly different, 2.30mm to 2.29mm, but will 0.01mm really make any difference? Almost saying are 10 and 9 speed chains actually the same?

I wouldn’t. It’ll work, but I’d expect dodgy/ghost shifting.

Trying to think of situations where I might try that and can’t think of one that doesn’t involve the world being overrun by genetically-mutated rat-spider-pigeons.

I wouldn’t even try that with 10sp links.

Any difference in wear will have that section of chain slipping & jumping.

It’s just not worth hurting yourself or the bike.

I did it, and it worked perfectly. But it’s clearly a horrible bodge, so I undid it when I got the chance. I think mismatched wear’s more of a concern than 9 vs 10 speed, and as stanleigh says it can be pretty bad.

OK, just an idea to save trashing a reasonably new chain… to the bin it goes 🙁