OP:
As @carlsbad2 said, not offended, and tinkering is a way to learn, BUT...
1 - DIYaudio is THE premier place to ask for advice on speaker mods.
2 - Your questions make me see you are not ready for this project yet. You need to learn how to do an electroacoustic analysis of the speaker, and be able to use that data to feed a crossover simulator. Go look at Troels Gravesen's site and his modes for the Yamahas or B&W speakers. You'll get a much better idea of what is involved.
3 - I strongly encourage you to reduce your tears by doing a straight up DIY build. Lots of kits already made, and you won’t ruin a perfectly sellable pair of speakers. Alternatively, buy a pair of speakers without working tweeters and learn to adapt a random new tweeter to them. That’s a lot nicer way to learn than on a perfectly good pair. You’ll feel a lot less like a mad butcher that way.
Best,
Erik