How to use diffrerent DE's on Slackware
 

Slackware's xinitrc is a lot different than arch's. How would I add another DE to xwmconfig that I compiled from source. And don't mention slackbuilds.org or alien bob's repos

You'd have to create a relevant file in /etc/X11/xinit/
eg. xinitrc.i3 or xinitrc.awesome

Do I need to put anything in them? Like a script?

Yes, you do. Look at the existing files there to get an idea. Which wm are we talking about?

Awesome

Have a look here for a basic entry for Awesome