Retrofitting split air conditioning in a kfw55 house

Exactly, the KfW says that no changes are to be made to the house within 10 years

No, not like that. Nothing may be done that destroys the KfW 55 status or its requirements.

But nowhere is anything more concrete described, like whether/how the split air conditioner is considered in a calculation.

That does not have to be stated anywhere, because only a planner can say that. Normally, if an air conditioner was not planned from the beginning, e.g., due to heat protection, the air conditioning system will not change anything afterwards. I actually do not know anyone who went the planner route. At least not if the air conditioning system was simply retrofitted. Therefore, I stick to my statement: Do it.

Hello,

I would just call 3 energy consultants and ask.

Maybe the topic is trivial in the end. I don't think an air conditioner has a big impact.

I assume this question is already answered. The bore size is the lesser issue (20mm), the appearance on the outside is usually the deal breaker

For a typical split system you already need 50mm