Whenever I choose to install some packages with the YaST software installer, it closes as soon as the software is installed. Is there a way to keep it open instead? 
Have a look at
Yast → System → Editor for sysconfig → System → Yast2 → GUI → PKGMGR_ACTION_AT_EXIT
I’ve just discovered the solution by myself:
YaST / System / Editor for /etc/sysconfig
In the editor:
System / YaST2 / GUI / PKGMGR_ACTION_AT_EXIT
Change the value from “close” to “restart”.
Thanks! You can remove my answer, since its only doubling what you’ve posted…]