If I break the 24 word seed with 256 bits into two 12 word parts, can I safely store them in two separate locations like I can with the seed extension?
You could, but using a 12 word seed and 12 word extension is preferable to splitting a 24 word seed in half. If an attacker finds half a 24 word seed, they will not be able to recover it, and so will know to keep looking the other half. If an attacker finds either your 12 word seed or extension, they will be able to recover a wallet. Further, if you put a small amount of funds in these two wallets, then if gives you plausible deniability that these are all the coins you own if someone finds one of your back ups or forces you to reveal your wallets.