I think Adam was asking how to change the umask value for all processes that are trying to operate on the /opt/lampp/htdocs directory.
The user file-creation mode mask (umask) is used to determine the file permissions for newly created files. It can be used to control the default file permissions for new files.
so if you will use some kind of FTP program to upload files into /opt/lampp/htdocs you need to configure your FTP server to use the umask you want.
If files / directories need be created, for example, by PHP, you need to modify the PHP code:
<?php
    umask(0022);
    // Other code
?>
If you will create new files / folders from your Bash session, you can set umask value in your shell profile ~/.bashrc file.
Or you can set up a umask in /etc/bashrc or /etc/profile file for all users.
Add the following to the file:
umask 022
Sample umask Values and File Creation Permissions
If umask value set to    User permission     Group permission     Others permission
000                            all                 all                   all
007                            all                 all                   none
027                            all             read / execute               none
And to change permissions for already created files, you can use find.