Will installing the Roundcube One-Click affect current emails?

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 customisation 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 Web Hosting and VPS.