If the licence giver believes that you're violating the contract, they are free to try and enforce that contact in court. A German court would almost certainly rule that the clause is unenforceable at least as it applies to that particular order-related modification (the licence requirements would still be valid for unrelated modifications). There is a nontrivial legal question whether that would imply that the requirement voids the licence as a whole or just the specific clause. Specific terms (e.g. AGPL clause 12) may suggest that it would void the whole licence, but I wouldn't be certain on how German courts would consider it given these specific circumstances; a German lawyer might have a good idea but I do not.
But in any case, contractual obligations are not an excuse for noncompliance with other legal requirements. If it does turn out that executing the order is incompatible with a particular license, then you must execute the order anyway and decide what's the best way to handle the consequences. Breaching a contract is a legally valid option as well, and in some cases that may even be the best option, if the expected liabilities/damages are less than the consequences of complying with it.
This is a death blow
So you'd just [be required to] keep a non-open fork of that code even if the license (e.g. AGPL) would prohibit that.