SharePoint Site Policy - notification message

Hello, I am starting to play with Site Policies on SharePoint site (SharePoint Online). One of my objective is to put a site in read only. 

I encounter the following issue : If I put a site in read only (with or without deletion), I got the following message : "SharePoint sites are read-only right now while we do some maintenance" ... which is not very user-friendly...

It seems strange for me.

I excepted to have "This site is read-only at the collection administrator's request" (message received by site owner in the site settings page) or to be able customize this message (I did not find anything in the UI, PowerShell Pnp, SPO or through CSOM).

What do you think?

Thank you in advance