To update or not update agent? If update, how to break news?

You should absolutely let him know. You may also want a refresher on why he chose the sum assured and his rationale for the WL policies.
Do note that the IR in BTIR is meant for self insurance and not for retirement/general wealth accumulation.
So the IR replacement to your WL is meant to cover any insurance needs in old age after you most probably stop working.

And lastly your portfolio allocation will shift to a conservative portfolio after age 60 or so, and a WL policy returns that's meant to adjust the base cover for inflation grows at about 3-4% which is already a conservative rate of return, without you needing to worry about your investment performance return.
Every year your WL policy gives you bonuses, you automatically "take profit" unlike your investments where you have to sell to realise capital gains.

I feel that you should and your agent will probably appreciate you for doing so instead of stopping the policies and going silent on him/ her.

But BTIR is not for everyone, have you actually done the IR for one year at least and confirm your strategies are sound before BT? One year isn't long but at least it'll give you a sample before confirming that you want to go down that path. It takes more guts and time than people see.