This change has no impact in the system’s current behaviour.
Is the preposition in grammatical here? I think we should have used on instead:
This change has no impact on the system’s current behaviour.
But I’m not sure if both are acceptable and have their own meaning.
The two constructions follow the forms below:
impact on <object>
impact in <scope/context>
The president has an impact on world politics.
Here, world politics is the object of impact.
The president has an impact in world politics.
Here, world politics is the context in which impact is made. This distinction with the previous sentence is more evident by rewording the sentence as
In world politics, the president has an impact.
and noting that the object of impact is unspecified.
In the OP’s examples, because there is no phrase indicating that system behavior is being used as context or scope, the native English speaker would assume it to be an object and use “on”.