Ahh I see. For that you would have to give the keypair to the user of the other node If you want to make it without onchain transactions. This would mean two people have access to the keys. It would also mean a change of the contract with the other end of the channel so maybe consensus should be needed.

It should be possible to do it with only one onchain transaction instead of two though.

One end of the channel could pay for a special mainchain transaction and the other end can decide within the htlc-time if he wants to accept the change or close the channel.