Unfortunately no, you are not allowed to have 2 in-force and active WalletSafe certificates at any point of time. Once you switch to the new plan via TNG eWallet, your existing WalletSafe certificate will be automatically cancelled and you will be issued with a new certificate of the new plan upon successful payment made on the same day.
Kindly note that premium of your existing WalletSafe certificate is not refundable upon switching to the new plan.