the hole is not a matter of cosmetics, it's a amatter of speaker function. it severely compromises the sound. think of it like sitting a speaker on the floor. you'll have sound off of the back of the speaker coming back through the hole.This severly compromises your midrange/midbass responce.
I'm quite familiar with kappas as I've sold them and still deal with them quite regularly. Actually I've got a pair in my car right now to get me by while I build my kicks. and yes they've got an external crossover-like thingy (not really a true full crossover, but atleast it's something) Again, the tweeters don't simply jsut disconnect, there is a interlocking design+alot of sometimes strong glue holding things together, generally it blows up the housing when you try to break the tweeter off. I'd honestly say it's kind of a roll of the dice. we went through 3pairs of kappa's to try to get one good set of tweeters for a friend to try a heavily attenuated very high crossedover imaging-supertweeter setup. The other thing is the amount of prying we're doing sometimes cracks the baskets, etc, AND we've got the extra leverage of being able to push aside/rip the screwdrivered cones but again this never matters since these are blown/warrentied/destroyed speakers we're dealing with.
I know precisely what you're wanting to do, and have done it (albeit for different reasons) and again there's NO benefit in doing this, and you're only risking messing things up pretty severly and there's no real gain to be had by moving the tweeter elsewhere. Hell, if you weren't in germany, I'd send you a couple pryed off tweeters... Beyond that, kappa tweeters are notoriously harsh. if you want to say sail-panel mount them that will only exaggerate this. Andother problem you're going to have is in mounting the tweeters. there's no real way short of gluing to mount the tweeter.
If you're deadset on doing it, have at it. I really don't even know what kind of advice in accomplishing it to give you. I'll see if we've got any blown kappas floating around, perhaps some new metalheads have cranked their gains again...