Self-consistent core-scrape-off layer numerical simulations of an ASDEX-Upgrade discharge where the nitrogen (N) seeding is gradually replaced with the krypton (Kr) seeding during the plasma current flat-top phase are presented. These simulations are performed with the COREDIV code focusing on the prediction of the impurity evolution (W, Kr, N) with matched global plasma parameters: total and core radiation, temperature at the target plate and W concentration. The numerical results are compared with experimental measurements for shot #30503 at three different time points: 2.5 s (only N seeding), 4.2 s (N + Kr seeding) and 5.2 s (only Kr seeding). The calculated electron temperature at the divertor plate can be reduced to 3 eV with the highest Kr seeding. A good agreement between modelling results and experimental observations is reported.