Olaf, are these Renner action parts a great deal different than what comes on a piano, for instance on my Yamaha. You probably don't know what's in my piano, but do you think the action is much inferior to Renner? Do you have any idea how much it costs to replace these parts? (I think you did it yourself, right?)
No, I did it not myself. I never would take my hand on my Steinway (only for smaller retunings if some notes start to wobble too much, and only on my Upright I try to do some maintenance myself).
I don't know how different the action would be, but I can say that the action in my piano is very easy going, the downweight of the keys goes from 47 to 49 gramm from right to left side, and really very good balanced. The keys go back very fast too. This, combined with the new hammer felts and intonation, eases to play soft. This is the main difference I see compared to the 75 years old worn out hammers. I also don't know the costs, my acoustic restauration with that Renner action, new strings, soundboard restauration, intonation took about 9.500 Euro, about 12.000 US-$. That is lot of money, but I have an acoustic seen new Steinway, and I swear, that is the best used money I spent so far, and am still happy after 2 years of the restauration.
You should ask an independant piano restauration factory. I even don't know whether every piano brand is suitable or that it is recommended for that action. But I know that Steinway and Bechstein have Renner actions by default in their pianos.