There are significant differences between the AER RGB 2 fans you propose to use, and the AER P120 fans supplied with the Kraken Z73 system. Comparing those at max speeds, the as-supplied AER P120's can deliver 73 CFM airflow at no backpressure, and deliver some airflow up to a max backpressure of 2.93 mm water. The AER RGB 2 120's can deliver less airflow (52 CFM) at no backpresssure, and keep delivering some airflow only up to 1.35 mm water backpressure. Recognize that the backpressure spec is important for the airflow resistance offered by a finned heat exchanger (the radiator). Those specs tell us that the replacements you propose will significantly reduce the ability of the Kraken z73 system to cool your CPU - they will allow proper cooling at low to moderate workloads (probaly using higher fan speeds), but may not be able to do the full job at high workloads.
Now, NZXT DOES supply those AER RGB2 120mm fans on another AIO product, the Kraken X73 RGB. I can't tell from their web pages whether their RGB model merely allows for this lesser capability, or the Z73 non-RGB model is over-cooled, or they have used different radiators with different airflow resistance between the two models. The spec I could not find is the maximum heat removal capability of the two systems - usual label for this is max TDP of the CPU it is suited for. Maybe you should check into that detail.