I like my kimchi mild.
(Does 'mild' modify kimchi? What is the opposite of 'mild'?)
Yes, it modifies kimchi.
The opposite of mild is spicy or hot, something like that.
1. I like my kimchi which is mild.
2. I like mild kimchi.
(Thank you. What about the sentences? Are both the same?)
Yes, they are correct, and they're interchangeable, too.
Yes, in the given sentence, "mild" is used to modify the noun "kimchi." It indicates that the preference for kimchi is to have a less intense or spicy flavor.
The opposite of "mild" is "spicy" or "hot." Using the opposite term, you could say, "I like my kimchi spicy" or "I prefer my kimchi hot."