how to add a custom domain to long live channelid other than live?

[yangcheng]

The use case you're trying to solve

as it's mentioned in the doc. ChannelID has one use case,

You usually want to leave this blank so that each PR gets its own preview channel. An exception might be that you always want to deploy a certain branch to a long-lived preview channel (for example, you may want to deploy every commit from your next branch to a preprod preview channel).

I want to have a preprod.example.com pointing to the particular preview URL. which current contains a random hash.

Change to the action that would solve that use case

I can set a custom domain either in firebase console, or via yaml file if I have *.example.com verifed.

Other considerations

[Adyaapatil09]

Yes that would be useful.