1. I like kimchi mild.

(What is the part of speech of 'mild'? Is 'mild' an objective complement?)

2. It touches rough.
3. It feels rough.

(Are both the same in meaning?)

I would phrase #1 this way: I like my kimchi mild. OR I like mild kimchi.

"Mild" is an adjective, whether it's before or after the direct object. An objective complement needs to be a noun.

#2 is incorrect and not used at all.
#3 is correct.