SF Grand Piano Home tweeter upgrade

You're correct Kehut, AG is not really a DIY site. Perhaps you would be better served asking this question on one of those sites.
Pehaps somewhere like here.

I own these speakers for 8 years but would be reluctant to try.
Coherence with the 2 mid bass/mid range drivers is more important in voicing a speaker in my mind.
If the tweeter seems splashy, better resistors (Duelund graphite) and better capacitors (Obbligato gold) in the cross over + clean source, amplifier and better cables will tame the tweeter and smooth it out. It will still be lively and will add air (a good thing and part of the speaker's sound) but will not hiss at you or emphasize sibilance.
My two cents.

I have been rather satiesfied with my SFGPH (the second version) and compaired it with many speakers (Usher mini 1 and 2; Dali Helicon 800 and so on) and they have sounded better IMHO. I have also stabilized the clip-on interface of the tweeter with a few drops of UHU-glue. The tweeter seemd ok until one day I played agressive Chopan piano music rather loud (16-20 db on the amp). Then I heard a kind of buzz (that disappered for a while when I pressed the tweeter gently with my finger). Then I decided to stabilized it with the UHU-glue and it got much better.
The set-up is Shanling 80C 2x monobl. and REL sub / NAD M5 and AARON pre-amp.