Can i travel on a valid H4 visa before approved F1 visa kicks in

Hello,

1>> I’m on H4, and applied for CoS for H4 -> F1. Got F1 approved and I-797A.
2>> My F1 Start date on I-797 is, say Dec 2014

*** Questions ***

1>> Can I travel outside US and re-enter US on H4 - before F1 start date on I-797A (before Dec’14)?
I don’t want to go through the F1 stamping

2>> At port of entry, would the Visa officers question me or see my visa status changing to F1 on 15th Dec?

Do I have to get F1 stamped, if I’m entering US before my F1 start date (while I am technically still on H4)?

Thanks in advance!

Regards,
Pooja!