Increasing variety of rolling stock? Options

[ddedicos]

I have enjoyed using AG on several of my routes, but this is my first post to the forums. My question is, can the amount of rolling stock available for activity creation be increased for more variety? In other words, if a route template is created to use, say, 10 box cars, can that number be increased to 15 or 20 to allow for more variety in activities? How could this be accomplished? Thanx for any help on the subject!
Doug