I've setup my Contacts (x51v) in various categories.
How can I customize it so that when I open the Contacts, it displays a specific category?
Ex: I changed filtering to Personal.
When I switch to another program, then return to Contacts, it reverts to All.

I don't think you can, but you can press the contacts button again and it will cycle through the categories. So if you know that the Personal category is the second one you just press contacts twice (once to open and the second time to move to Personal).

Always read stuff that will make you look good if you die in the middle of it.