Stacking ZYXEL XGS 2220 54HP

Hello,

I recently acquier 3 Zyxel XGS 2220 54HP, i have stack my swtich with DAC10 cable.

Once i activate stacking mode, i can't configurate port 51-54 with VLAN.

I want to use the last 2 ports (53 and 54) for stacking and the other for SFP fiber VLAN for other switch connection. It that possible ?

I saw on the notice it said : "This is the port index number. These are the default stacking ports (the last four ports of your Switch). They are reserved for stacking only."

Thank you.