Using this method for the score/new life will be much more difficult than the every Nth click event you mentioned in your first post. Scores rarely hit exactly on the value you earn a bonus for. You usually get it when your score is greater or equal to the necessary score. For this situation, I would suggest you set a LastBonus variable and check where Score >= LastBonus + 100.
I was suggesting the method again for the click iteration situation. In that case, the user will always click a 5th, 10th or 15th time. You can't skip from clicking 4 times to 8 times. The (VarScore % 100 = 0) means the score has to be an exact multiple of 100.
For the last question, yes. If the variable you are testing starts at 0, the Modulus will start as true so the user would get a new life immediately. There is however, a way around this by adding a condition that says score != 0.