H4 to F1 COS, re-entry on H4 on possible F1 stamping issue

[anandbahety]

Hi,
I came to USA on H4 in 2014 visa and H4 stamp on my passport is valid for sep 2015. I did a change of status to F1 in USA and started studying. I plan to go back to India for F1 visa stamping. I have a few questions on my return in case there are issues with F1 stamping
1. Can I re-enter back to USA on H-4 visa stamp I already have and valid till september as long as I travel within its validity ?
2. Do I need to do any document processing or any conversion back to H4 as I did a COS to F1, to re-enter or basically just use my current stamped visa to re-enter? 
3. What happens to F1 COS if I enter on H-4 ?

Thanks