How to correctly modify virtual host settings?
You can change the settings of virtual hosts running on the Plesk. For example, you can set custom error pages (similar for all virtual hosts), or change the port on which the hosted site is available by creating custom configuration templates.
See this documentation for more instructions:
Important: Do not change the default templates. To introduce your changes to the configuration, copy the templates you need to the
/usr/local/psa/admin/conf/templates/custom/ directory, preserving the directory structure, and then modify these copies. You can create new templates from scratch and place them in the
custom/ directory according to the default structure.