Hmmm... with four days I would probably recommend the 1.e4 starter course as it is quick, to-the point, and free(!). Of course, this also would depend on where your repertoire is now, are you well-versed in 1.e4?, do you feel confident in your understanding of the Sicilian? In my opinion, four days would be just enough time to rewire your repertoire. This being said, It very much matters on the circumstances of the tournament; is it a 2 hour game or rapid time control? what is your rating? do you have lots of time to study? there are a lot of variables. As it turns out, I am in a similar situation, I have three weeks to prepare for my first FIDE tournament ( I am 1930 or so USCF) and I am undergoing some repertoire changes. In conclusion, lots of variables come into play but I think 4 days should be, with the right mood, enough time to get the job done.
Looking forward to your reply, BK
4 days and low (sub 1500?) rating. Forget repertoire, or at least anything significantly new in that area.
Make sure you learn basic pawn endings, basic rook endings, practise check mating patterns, tactics, the openings you know: check you can still get to a middlegame in the main lines (i.e. avoid the traps) and have some idea of what to do (a few model games).
That's probably it. You'll win games based on outplaying and at the level you are describing, it'll be tactical and following the basics to get a good position will give you a chance. Where you lose it'll be more likely a trap or missing tactics.
Chessmood repertoire takes months to work through properly even if you are full time.