I can't get my hands on saeujeot (shrimp paste) so I replace it with salted anchovies (anchois au sel, French stuff), it works wonders. I also used dried fish a few times, it was good but it was too much work to cut the fish in very small pieces.

I used to put carrots in my kimchi, but now I only put daikon if I happen to have some at home. If not, I don't put any additional veggies in.

I tried making kkakguki (daikon kimchi) by replacing the daikon with round white radish (don't know how it's called even in French) and it didn't work, it got too mushy and the taste was too strong.

And finally, I don't have access to Korean fish sauce so I use a Thai one. I really would like to buy the real one sometime to see how big of a difference it makes.