Repayment change needed? Or better terms?

Usually, you are allowed to repay 5% separately. Was that not enough?

not with us, such an option to increase or also reduce the repayment can sometimes be needed.

Best regards
Sabine

Is the assumption that having a repayment rate change in the contract results in a higher interest rate justified?

Yes, it is always factored in like the special termination right. But you don't really notice it.

No one needs an increase in repayment. Prepayment is enough.

Possibly, the increase in the repayment rate could still have a positive effect on the calculation of a prepayment penalty.
I am sure that prepayment must be taken into account.

We chose our installment 7-8 years ago with a 2% initial repayment rate so low that almost all worst-case scenarios (possibly with restrictions on vacation/car etc.) can be covered. The rest of the repayment should then be made through prepayments.

In our case, the financial situation has developed significantly better than expected, and fortunately, all worst-case scenarios have not occurred so far.
Since my wife returned to work after parental leave with 35 hours, more hours than originally assumed, and both of us had significant salary increases, we were able to use the full 5% prepayment option at the beginning of the year every year except the year of construction. Planned were annual prepayments of 2-3k € per year, provided none of the worst-case scenarios occurred.
Unfortunately, the 2-3 times repayment rate change was not yet standard for us; otherwise, I would have adjusted our repayment rate since the next prepayments for 2021-2023 are actually already prepared.

For people who still expect significant salary increases or for couples planning to have children or for entrepreneurs with highly fluctuating income, I would definitely consider adjusting the repayment rate alongside prepayment as a useful tool.

because the next special repayments for 2021-2023 are actually already available.

A nice windfall.
If you manage to invest the excess assets at higher interest rates than you pay on loan interest, then the change in the repayment rate would also be irrelevant. That could also be recalculated: repaid slightly faster, but with more expensive loan interest on the entire amount.

I do that partially with ETFs. For me, the interest rate is still almost 3%. You then have to generate 4.x before taxes. I could still pay off the KFW loan, but at 1.4%, it's peanuts in comparison. I actually just wanted to say that sometimes things turn out differently than planned – whether negative (in the form of loss of earnings/sale) or positive (salary increases/inheritance/lottery win) – and then flexibility is always good. Of course, always weighing costs and benefits.