No. My understanding is you're contract on $X per month. So with that said you can always go onto a higher plan and/or reduce back to your contracted amount anytime during that period. After your end date there's more freedom, as then can drop to a lower plan if need be.
Be best to have a chat with Optus directly as I'd hate to read that you inadvertently cancel your current contract ect.
Hey Dono - caaf is correct in that your contract won't restart, there also won't be a fee to increase your plan amount each month. You can chat with us on 133 937 or here if you're needing a hand still.