Two dramas that come to mind are Undercover and The Spies Who Loved Me.

My Fellow Citizens

I can only think of Healer.
May be School 2017.

The Spies Who Loved Me was really fun!

It's not a rom-com, but as I finished it two days ago, I have to mention Flower of Evil.

Gender is often used as a secret-identity trope, but usually between couples who aren’t married yet. Some examples are Love In the Moonlight, Coffee Prince, Sungkyunkwan Scandal, and Mr. Queen. And then there’s I’m Not a Robot, where the love interest in question hides from her sweetie that in fact she’s…not a robot.

I just read that there might be a Korean remake of the Japanese drama "Caution, Hazardous Wife." Premise being an ordinary housewife with a hidden mysterious/violent past uses her very special skills to help the women in her neighborhood.

Flower of evil

I'm watching Witch's Love right now. There's a romance with a secret identity (and secret powers).

🔸Perfume (The female lead changes appearance and her true appearance is a secret)
🔸🌹 Rose Mansion(This is a thriller)
🔸Fan Letter ✉️ ( a short fluffy drama)
🔸The Golden Spoon 🥄
🔸Shop King 👑 Luis( ML forgets his chabol's identity, cute drama)
🔸Moon 🌚 Embracing the Sun 🌞 (A saguk)
🔸Hotel DelLuna
🔸Coffee ☕ do me a favor (Same as the above, but here the FML uses coffee to achieve her ideal appearance)
🔸Anna(Here the entire true identity of Anna is a secret)
🔸Curtain Call(The lead pretends to be the grandchild of a conglomerate)This is actually finished pretty recently
🔸You are beautiful ( FML pretends to be her own brother)
🔸Your Honor⚖️(ML pretends to be his judge brother)
🔸Mask 🎭 (FML pretends to be somebody else completely unrelated to her)
🔸My Holo Love❤️(ML pretends to be a holographic image which is loved by the FML)
🔸The painter of the wind( an old saguk wherein the main female character wears men clothing to be able to paint)
🔸Sweet Munchies👩‍🍳
🔸A business proposal ( The secret is out half way through the drama)
🔸Lie after lie ( There are many secrets here ... one is the secret identity of the FML and it is quite big )
🔸That Winter ❄️, the wind 🌬️ blew( ML disguises himself as the FML's brother)
🔸Fermentation Family (here tge love story is only one among the many)
🔸The king's daughter,Soo Baek Hyang
🔸Come back Mister(A father comes back after death to help his family, in somebody else's body)
🔸49Days(Same story but the ghost character is a female and we have three love stories)
🔸My Girl (Here the leads know the secret identity. They work together to keep the secret from others)
🔸Secret Garden(Body switch, same as the above)
🔸☕ Coffee Prince(FML pretends to be a boy)
🔸Train 🚂 🚃 (Parallel word's being substitutes others similar to him)
🔸Dongi(A saguk in which the FML is in hiding due to her dad. He was framed so his daughter went into hiding)
🔸 Jewel 💎 in the Palace (similar story but here both mom and dad were in trouble)
🔸Be with You(This is actually a movie and the FML experiences a parallel world)
🔸Mouse(I am not going to spoil this)
🔸Black🖤(The ML is a grimm reaper)
🔸Blood(ML is a vampire)
🔸Love in Sadness(Thr ML helps FML changes her appearance to keep her safe)
🔸Orange marmalade (FML is a vampire)
If we don't limit ourselves to Kdramas:
🗡️ Hotarogusa( a delicate story about a girl who tries learn swordmanship in old japan, to prove his Samurai father's innocence. this one is short and very beautiful ❤️)
🔸Romance with the Blind master
🔸Love between fairy and Devil 👿

Honey Lee’s upcoming sageuk, “Flower That Blooms at Night” sounds like it’d fit in this category.

What if we put the shoe on the other foot and ask about a secret identity which is not only not hidden from the spouse but was actually her suggestion? That secret identity created that way lies at the very core of the great family weekender FATHER IS STRANGE.

The best kdrama based on this premise is FLOWER OF EVIL! A suspected killer who took on a new identity and married a detective--what a premise, with lots of plot twists. Just watch this one, fellow beanies. It is highly rated and available on Viki and Netflix.

Another one of my favorites is THE CROWNED CLOWN--evenutally the Queen found out! Also available on Viki and Netflix.