Hi isn't I.M.'s real name Im Chang Kyun, not Lim? (hence his stage name I.M.)
The character for I.M’s last name, 임, can be romanized as both Im or Lim, and corresponds to the same hanja character 林. Although there is no ㄹ (r/l) in the character, the L sound exists somewhat as a soft consonant in speaking. It works in the same way that the common last name 이 is romanized usually as Lee even though the korean syllables only make Yi/Ee (no L). We’ve seen Lim used more commonly in profiles and thus chose to use this spelling, but his stage name also does correctly correspond to his last name.