Apple TV one year trial

I think since you first logged in with your old id, now you can't do it again with the new id. You first bought the device and logged in. After this is considered that this devices is already activated. It does not offer unlimited activations, otherwise people would make several apple id's and watch for free as long as the offer lasts.

But, if its any way you can transfer this ( and i think it's not) only apple knows. So, contact apple support :)

No. The 1 year free like other purchases and subscriptions are tied to the Apple Id that redeemed it and it cannot be transferred.

And since you already used it, you cannot redeem it again on a different Apple ID.