If you want to prevent your customers from importing sites from SiteBuilder 4.5 hosting accounts, you can remove the Import Site from SiteBuilder 4.5 button from the editor. This can be done by adding a line to the configuration file %plesk_dirsbconfig.
To make the site import functionality unavailable to users:
On the hosting server, open the configuration file
[general]section of the file, add the following line:
show_import_site_button = 0
Save the file.