In your case, Increase the number of partitions on an existing topic will have an impact on how the message will be dispatched into partitions.
I mean if you use the default partitionner, and your message have key, the algorithm is 'hash(key) % number of partitions' That means that a message with the same key, won't go into the same partition, before and after the change. IMO, It was important to notice, in case you need ordering by key. Jeremy
