No.
The Roundcube one-click install provides a separate installation of Roundcube for you to manage, send and receive emails. This won’t affect the standard stackmail.com webmail application.
As third-party software, we can’t help with the customization of this software, but it can be used to create a more bespoke webmail client.
Our one-click install for Roundcube is available with our Shared Hosting and VPS.