Hi Tjark,
As far as I know it is not possible to do this using out of the box page title.
You can do a work around by adding custom styles to disable pop-up header that show page title (see example SCSS code below), add ‘no-header’ class on pop-up. On the pop-up page add your attribute in a container and give it a class name called ‘custom-header’. Make sure to compile your SCSS code using Calypso.
.no-header {
.modal-header {
display: none;
}
.custom-header {
background: #ddd;
padding: 10px;
margin: -20px -20px 20px -20px;
font-size: 18px;
}
}
Hope this helps!
as of 8.12 it is out of the box possible to override the page title dynamically