You can only alter the two offsets:
PHP Code:
set_pdata_float(Entity, m_flNextPrimaryAttack, delay, XoWeapon)
set_pdata_float(Entity, m_flNextSecondaryAttack, delay, XoWeapon)
Anyway, what I did was only to do what the game does(if you look at what I linked, you will see the same code).
You can count the attacks and set the offsets after 3 attacks. CountDown is not needed as game calculate the next fire time automatically, you will have just to display the message.
One more thing,
CurWeapon event give you the player index, there is not point in looping all players.