How many times you thought "Why even in 50 games match do I get double openings with this huge opening book? Should I try an even larger book? Or may be tweak the variety slider? (Thus getting more frequent unbalanced openings too)"
Here is one possible solution. This site provides a random duplicate-free sample from your favorite opening suite. Just select an opening suite, and the number of positions, and click "Sample".
Copy-paste the output into a .pgn file (Ctrl+A, Ctrl+C, etc.) and choose it as an opening database in your tournament GUI. If you'll use each position twice with alternating colors, you need just N/2 positions obviously.
More information at link
This tool is made and hosted by Kirill Kryukov. All included opening suites are made by their respective authors. Ray Banks and Adam Hair contributed ideas and inspiring discussion.
PGN files can be downloaded here.
Other related tools:
•PGN-Selection by Volker Annuss and Frank Quisinsky. I'm not sure if/where it is still available, but here is a CCC thread about it.
•ChessGUI has similar function, according to Matthias Gemuh (message)