Welcome to Audioholics Alexandre. You didn't actually ask a question, but I assume you meant to ask if replacing the dead Polk tweeters with the Tang Band 25-17119 tweeters will work.
The short answer is no, it is highly unlikely that the Tang Band tweeter would substitute for the Polk. More is involved than than the resonance frequency (Fs) and size of the face plate. The crossover from the mid range drivers to the tweeter was custom designed by Polk for that combination of drivers. Unless the Tang Band tweeter is identical in performance to the Polk tweeter, a substitution will change the performance of your speakers. Whether it sounds better or worse is unknown. $90 each is a high price for the Polk tweeters, but unless you find them cheaper somewhere else online, its less than replacing your speakers.
For what its worth, I looked online and found
these Polk tweeters at $40/pair. The description says they work in the Polk RT speakers, including the RT5, RT10 and RT12.
Parts Express sells Tang Band drivers including
the 25-1719S tweeter. Is that the same as the '25-17119' that you mentioned? Look closely at the dimensions of the face plate. Is it the same as on your speakers? One of the customer reviews said "Great tweeters. I use this to replace the tweeters of my Polk Audio Rti12 towers, (one went bad) and this ceramic tweeter are smoother. The sound is more balance, and the detail is still there. The original Polk tweeter were in my opinion bright." I don't know whether this person understood what he was doing or not.
If you think your speakers sound 'bright', making it less bright sounding may be as simple as adding a 1 or 2 ohm resistor between the plus terminal of the tweeter and the wire running to it from the crossover. That should work better than trying to alter the sound with the AVR tone controls. Of course, you need working tweeters to do that.
It is unusual (but not impossible) that a crossover got fried by your friends karaoke mishap. How do you know one of the crossovers is dead?
In the future, don't let friends plug a microphone into your system. A microphone will always pick up sound from nearby speakers, and feedback will result. Home audio speakers were not made for that.