KfW funding approval - Are changes to the house possible afterwards?

For the credit variant, there are various dates in the contract at which it is checked whether all documents are available (=submit 3 months in advance) and then the payment is made. The first date is 2 years after the contract start. I assume that it works similarly for the grant variant. You can then use it for everything: vacation, new car, garage, special repayment,...

Another question would be: Do I have to report the recalculation to the KfW then? Is that stated somewhere?

I have now actually found it: "The KfW must be informed as part of the proof of project implementation if the project has changed or if other funding-relevant parameters visible from the respective product sheet have changed." (p. 1 General Terms and Conditions for the application and granting of subsidy products of the KfW via the KfW subsidy portal)

I assume that it works similarly for the grant variant.

Not quite...: "The payment of the grant takes place after a positive completion of the review of the “confirmation after implementation” (BnD) into the account of the grant recipient. This normally takes place at the end of the month following the review." (p. 11 Information sheet Application BEG Residential building grant Efficiency House 461)

The "confirmation after completion" is the decisive confirmation and may differ from the confirmation of the application (BZA). I have experienced this often in renovations, even a KfW house change, because the building was designated as a listed building in the meantime. There are also energy consultant changes and subsequently different approaches.

The "confirmation after completion" is the decisive confirmation and may differ from the confirmation of the application (BZA). I have often experienced this during renovations, even a KfW house change, because the building was designated as a listed building in the meantime. There are also changes of energy consultants and consequently different approaches.

What do the energy consultants/construction supervision cost? How much do you have to deduct from the subsidy for the consultant?

We have already been through all of that. Both the question and the answer. So again: Go into the race with €5,000, you will get 50% additionally refunded through a separate KfW program.

Otherwise, just ask your developer!