Permissions can be setup from the File Manager feature in the Plesk control panel. But they get reset to default because Plesk runs an inbuilt tool [websrvmng] everytime on all the domains to check the file & folder security. If you want to assign customized permissions on certain folder, please open up a ticket with our windows support or do come on live chat support, we'd setup those permissions manually & directly from the server [& they won't be reset back]..
