I recently finished watching Healer and for the most part I absolutely loved it, but now I'm trying to find dramas similar to it. Specifically, dramas that have characters with secret identities like Jung Hoo's identity as Healer and/or the way he disguised himself as different characters throughout, like Park Bong Soo, during his mission. It was really fun to watch, and I loved seeing it all unfold. Honestly the first half of the series was my favourite part to watch because of it. So if anyone knows of anything with that sort of premise/feel to it I'd love to know!

Here is my personal list for dramas about Hidden Identity: http://mydramalist.com/list/p1R8KRy3
Among those dramas, the most fitting to your description are:
- City Hunter (korean)
- Myung Wol, the Spy (korean)
- Sai Lub Rak Puan (thai)
The most are dramas I've liked that don't match this exactly but still deal with hidden / multiple identities, but I don't know if it fits with your description. The ones with the questionmark behind it, means I don't know for sure anymore because I watched it a long time ago.

Birth of a Beauty.
You Who Came from the Stars
Liar Game (?).
Missing You (?).
Prosecutor Princess.
You're All Surrounded.
Angry Mom.
Please Come Back, Mister.
mask
200 pounds beauty
bride of the century
glass mask
heaven's promise
perfect couple 
that winter, the wind blows
the princess wei young
who are you: school 2015
you're beautiful
Bridal Mask
Cruel City
Angry Mom
Nirvana in Fire
Empress Ki