Once you start green card application can you still go back to F-1 status later?

You will have hard time proving nonimmigrant intent wht an immigrant petition in the workings.

When do we need a police clearance certificate during the green card process?

The NVC should have informed you abotu the need of the certificate. You should follow their instructions.

Got I 140 denial notice in 6th year of H1. Can we extend H1 on 140 appeal basis ?

I-140 must have been approved to provide for 3 year extention, I think.

Can I transfer New H1b before actually started working for an employer?

Most people believe that you must first get an H1B status to use portability provisions.

My Wife L2 Visa is expiring on 22nd Oct-15. She got picked in H1B Lottery which is currently in RFE state. Please let me know

She would most likely need to leave and consular process her H1B visa.

(E2 visa)can i swap jobs in ny? since my visa has the company name? apply again? do i need to go home apply from there?

You could seek extension of status as a business owner if you qualify or you can seek another visa at the consulate.

Is a 2nd biomatrix request really a good sign? Does it mean the case is moving forward?

USCIS official position is that they are now working on 2013 cases for affirmative asylum filings so you are probably correct, it should be a good...

Can Green card be renewed overseas due to medical reasons?

I do not believe that it is possible oversease becasue of the biometrics. You should indeed talk to the consulate.

MY NAME IS KEVIN AM A HIATIAN ON A TPS THAT IS DO TO EXPIRE SOON. AM GOING NUTS DON'T REALLY KNOW WHAT TO DO.

It is very likely the TPS for yoru country would be extended. Please do not panic.

When Federa Marshal is involved, it is probably a criminal investigation and you need to get yoruself a defense attorney.