Already done - it was no problem. :) The standard contract was still used as a basis, but it was corrected by the notary in several points.
Probably then a smaller regional builder? I don't have representative experience with developers, but my impression is that there is usually a very clear procedure and changes are simply not accepted. I basically understand that. If I sell 30 or more apartments/houses, I can't have every change checked first by my legal department/lawyer.
In the builder's purchase contract, I had the option to have a few brackets added because, in my opinion, an extremely complex sentence led to ambiguity. Otherwise, nothing was possible for us. One request could still be included in an appendix.