Redeem code live gold bonus

It will extend you current subscription

If it's a trial, then it wont work as you already have a gold subscription.

If it's a trial code, it will not work with a gold subscription so it won't let you add it. If it is just a regular gold subscription it'll just add on to the 1 year you already have.

It's a code that will give me the right to use live gold for 3 months. You can tell if it will add up to the 12 months I already have

If it's for 3 months then it's a regular code so yes, it'll add to the 12 you already have. You can add up to 36 months of gold at a time.