hobbles61:
can you select the order you golf balls will be put in play if you run out of balls you are using?
No.
WGT provides notification you are down to the last ball of that make/model, and the notification gives you the opportunity to get one or more sleeves of the same ball.
WGT is set up such that a make/model of ball different from the ball a game was started with can not be put into play mid-game. The lone exception is the free Starter ball WGT substitutes so you can finish the game in progress.
There is a Local Rule: Conditions of the Competition tournament committees can adopt known as the One Ball Condition that is covered in Appendix 1, Part C, 1., c. in the USGA Rules of Golf book.
http://www.usga.org/Rule-Books/Rules-of-Golf/Appendix-I/
WGT is the tournament committee here, and has modeled the Conditions of the Competition similar to the One Ball Condition.