One of the point about the NAP between Korea and Rome, is that (iirc) Korea was the one asking for a long NAP (specifically to prevent Rome from finishing them with its praetorian army after a 'short' NAP).
Regarding the possible gain from breaking this time:
Even with 8 praet away (and they would have to trust Spulla about the number), Rome has enough at home to prevent any major invasion and looking at production numbers, breaking the NAP will result for Korea at losing in a very short term all their mainland cities (capital+captured while breaking the NAP).
In short I would not break the NAP if I was Korea
(HRE, Ottoman or Rome on another hand, once spullla is crippled enough, having an opportunity strike on your closest neighbours could be more 'acceptable')
Regarding the possible gain from breaking this time:
Even with 8 praet away (and they would have to trust Spulla about the number), Rome has enough at home to prevent any major invasion and looking at production numbers, breaking the NAP will result for Korea at losing in a very short term all their mainland cities (capital+captured while breaking the NAP).
In short I would not break the NAP if I was Korea
(HRE, Ottoman or Rome on another hand, once spullla is crippled enough, having an opportunity strike on your closest neighbours could be more 'acceptable')