L1B to H4 conversion

Hi All,

I am currently on L1B visa and its expires in august this year. I am planning to apply for H4 (without EAD). Does L1B to H4 always COS or I can travel outside US post L1B expiry and reenter with H4 stamp ? And if its always COS, can I decide the date for H4 to be effective ?

Thanks,
Rohit