Under the knife
No, you do not need to surgically modify Koreans' tongues to enable them to properly pronounce their Ls and Rs. The "problem", if you want to call it that, is that the Korean language (like Japanese) draws no distinction between the two, so children growing up with these languages don't learn to hear the difference.

Americans of Korean descent who grow up speaking English seem to manage it OK. Doubtless many Korean adults have trouble with it; others find it learnable. And a lot of us dumb Americans have trouble with the complex tonalities of their language, too, for the same reason: We didn't grow up with a language in which it mattered.