Partially right because your host prepare all food for warm welcome.
I guess it' only works between Korean not to Foreigner, They will understand if you don't eat octopus, so don't panic.
However, just try to eat as much as you can. Korean really think hospitality importantly :)

Traditionally, you should wait until eldest start to eat meal and shouldn't leave until s/he is leaving.
Second, you shouldn't put your arms on table(But to be honest, I'm doing it haha)
Third, when you receive alcohol, put your both hands at glass or cup.
Fourth, when you drink alcohol, turn you head opposite site of elders.

Just few things are popped up in my head.
i hope you have a good time with your host family when you are staying at Korea :D

Don't sweat about that.

it's mostly between Koreans but even though I'm Korean, doesn't matter. If I can't eat something, I just say that I'm so sorry I can't eat the food but I'm so thankful for cooking for me.

Tbh because of you are a foreigner, it's more simple. If you don't mind, try once (or not it's up to you) and if you don't think you can enjoy the food, just tell them it's your first time to eat that one and you can't eat and say sorry and thank you. 

No one will be upset about it.