The F3 of those speakers is 33 Hz, and it has an 8" woofer. It will not make any difference if you plug the port with crossover above 60 Hz.
When you plug the port, you will have a sealed speaker with an over sized cabinet. It will likely raise F3 to 65 to 70 Hz. Damage would only occur if you plugged the port and the equalized the speaker back to an F3 of 33 Hz.
Your real problem is that you have a three way speaker with crossover to mid at 160 Hz.
So if you crossover at 80 Hz you will have two crossovers only 1 octave apart. At 95 Hz they will be less than an octave apart.
It is highly desirable to have crossover at least 2.5 octaves apart and ideally 3 octaves or more apart.
It is really difficult to get a smooth response will closely spaced crossovers and you almost always get a troublesome band pass peak.
In addition I think it is poor practice to design speakers with passive crossovers below 350 to 400 Hz area. The large value components tend to cause all sorts of havoc.
I suspect the benefit you notice is that you are getting much less sound from the woofer, which likely is suboptimal because of the issue I site.
So I would ignore the port issue, and play with the crossover point and see what sounds best.
You should also try using your speakers full range and bringing the sub in at 60 Hz and see how that sounds. If it were not for the problem of that low pass passive crossover that should be ideal.