Always redirect to SSL

If Always redirect to SSL setting dont take effect then make sure you have turn it off/on as per need the option Require SSL in Tweak settings.

Is it possible to modify the Tweak Setting from shell?

Yes, it is possible in order to do that you will need to edit the file

/var/cpanel/cpanel.config

After making changes you will need to update the changes made with :

/usr/local/cpanel/whostmgr/bin/whostmgr2 --updatetweaksettings 

This command will put any changes made to the /var/cpanel/cpanel.config file into effect.

The above settings in /var/cpanel/cpanel.config correspond to the following settings in the WebHost Manager in Main >> Server Configuration >> Tweak Settings: 

Tweak setting changes not taking effect

Sometimes saving settings in WHM > Tweak Settings doesn't seem to restart cPanel and WHM (whostmgrd) for the changes to take effect. So you will need to manually restart the cPanel service.

       

if webmail.domain.com not accepting credentials

I faced one issue as webmail.domain.com was not accepting username and password, however if I access webmail with domain.com/webmail then the username and password was accepting.

Solution :

In order to get this issue resolved, it needs to enable Proxy subdomains as below :
WHM >> Main >> Server Configuration >> Tweak Settings >>Proxy subdomains