Until recently I had the option to change paper size and orientation in the LibreOffice Print Dialog > General Tab, Properties Button. Now those options are disabled. And this is true for all 3 of my printers. It is also true on multiple computers.
In the last few days I have been trying to solve some (other) printing challenges. Based on various support suggestions, I have upgraded a number things. For example, I recently upgraded to LO 5.0. I am not sure when I lost the ability to set these two options.
I am running Kubuntu (12.04 on one computer, 14.04 on the other). My printers are HP X551dw and HP 8630. Driver is HPLIP 3.15.9 (latest as of today). All operating system updates are current as of today.