This is from 2011 news regarding our first order of Nagapasa-class sub :
"They are capable of launching torpedoes and
other guided weaponry through eight tubes."
What kind of guided weaponry?
www.koreatimes.co.kr
Launching sub-harpoon is rather a CMS upgrade for submarines. This is like telling the computer "here are new libraries (like drivers on computers) which tells you how to communicate with this new type of weapon and which kind of parameters are to be passed (depth, distance, target location, flight profile, etc etc.)
So it should be available,unless provider of CMS (i presume Germany) has locked it.
Why would they possibly lock it?: It was not included in the contract within price.
How long does it take to unlock it: less than an hour.
Does it make sense it to be locked: not actually, any submarine capable of fiber guided or modern torpedoes typically capable of launching sub-harpoons.
Sub-harpoons are actually a torpedo, big as a torpedo, wide as a torpedo, looks like a torpedo.
The effort falls in line with Pentagon efforts to deploy more punch at longer ranges, a clear recognition of the growing ability of China and Russia to keep American and forces at a stand-off distance
breakingdefense.com
The submarine interprets it as a torpedo,not a missile, except it requires a surface location to be loaded on the missile via interface.
But meanwhile i have seen some manufacturer limits some functions of a radar in software level just because the buyer has insisted for a lower price and later upgrades (literally unlocks) it in a maintenance or MLU.
Afaik, capability like this is something should be regarded as military secret.
Hiding this is like hiding which aircraft has been purchased or the missiles. Everything should be secret if you ask me,but at the other hand everything is displayed. Such as; if sub-harpoon was delivered it would definitely be showcased.