CrossFit can be used in place of short days.
The idea is to reduce volume, add different types of training, be stronger particularly on the bike and avoid or reduce repetitive motion injuries.
You will still need your long days.
This is pure speculation having trained both disciplines but I would guess subbing in the CrossFit will allow you to become a better triathlete up to a certain point.
Once you reach that point specializing will produce faster times. Most very good triathletes are lighter, thinner then what CrossFit training will produce.
What was your half time? What is your goal?