Can you damage your speakers by plugging bass port vent?

A ported speaker will roll off at 24 dB/Octave below it’s tuning frequency. A sealed box rolls off at 12 DB/Octave, typically a half octave higher. An optimally tuned system that’s flat to 40Hz will be -24 dB at 20 Hz. The sealed box will be flat to 60 Hz, -12db at 30 Hz. Ported systems are harder ( but not impossible) to tune properly and so their reputation.for boomy ill-defined bass. Sealed boxes reputation is for tighter but ’slower’, less lively bass. It’s way more involved than just sealing the box. But if you understand the basics it makes what you hear so much more comprehensible.

Re panzrwagn - Closed box sound is dryer because it ends faster, has less overhang. It's more detailed because it stops more quickly. Speed of bass is really not the initial attack but how quickly it stops and closed boxes stop faster. It's just that the extra overhang of reflex boxes adds richness like amps with high second harmonics that people like despite being less accurate.

With modern programs there are good reflex loadings(albeit less good than good closed loading). If reflex bass is too boomy it's either incompetent design or often unfortunately achoice to make a speaker sound bassy because that sells in way too many cases.

All that bass energy, builds and builds and builds until suddenly, "KABOOM!!"

+1 dynamiclinearity. The "ported speakers have slow boomy bass" is a proverbial old wives tale.

@OP, with the K6 being ported through the bottom of the cabinet, I'm not sure that you will find an improvement overall - yes you can reduce the bass extension, but you will change the overall tuning of the loudspeaker and probably not in a good way. Personally, I've never found that plugging the ports in loudspeakers results in  net overall improvement.

You would be better spending some money on some bass trapping and some absorption for the first reflections. Acoustic treatment is cheap and you can still use it when you move somewhere more permanent.

The only way I could get my R11’s to play nice with my F12SE’s was to plug my R11’s two rear facing ports with the KEF supplied foam inserts. The plugs lessen the bass, but don’t seal.
Frequency response changes verified with room correction software. Then used mini DSP on sub to further flatten. Very good results.