Yes, you can do that if you buy a engine like fritz or rybka. I got tired of the same lines so i got Rybka and fritz and they have an option to start up in a certain thematic position or one that you choose, sadly the fairly good engines do cost money though there are some free ones for download on thissite.
A suggestion about Play vs Computer
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I play the medium (1600) level a lot and I think it is good for my skill level - but I have noticed that it plays basically 2 lines (if you play white anyways) and that is a Sicilian Opening and a Kings Pawn opening. This is fine for me now since I need to work on both of these openings - however - it would be nice if you could chose the opening style you wanted to play. Has anyone else ever felt this way?