change default user of webserver for special directories

[Zowheni]

for example, if i'm using a php script that writes files, or using a cms , the files and folders that are generated are owned by a special user (f.e. \[code\]www-data:www-data\[/code\])is it possible to change this default user for special directories?so that for example all cms systems or php scripts in general use another user and group in the dir \[code\]/httpdocs/somedir\[/code\]?