Custom comments on domains and users

It would be great if each time we create a new domain or user, we could write our own comments on it, for example, write the contact information of our clients, or the date we created the domain, or any other custom information we like to write, so we can see that information on the list of domains/users… there could be a “comments” icon and when we put the mouse over it, it shows a tooltip with the text we wrote.

Right now I have to do all that in an excel file on my own computer.

Is this possible?