Need clarification on below scenarios
If extension is filed along with the H1b, then H4 dependent travel.outside of US, can biometric center be provided outside of US while filling the extension ?
If extension is filed and got the biometric date for H4 , is it possible to change the location outside of the US ?
and re enter after approval to US
I may not answer your question directly but I think, your H4 status extension would become void once you leave the country.
Reason: A Status exists while you are inside US. An exteions that you have filed is to Extend the STATUS. Thus, there will be no status once left US and any extension request has no meaning at that time.
Scenario 1 : Well, so far we have not see anyone do that yet. But technically, you may . check below screenshot from I-539 instructions that indicates that you can ask the embassy or consulate outside of US. CheckI-539 Instructions on USCIS.gov. In all reality, you can check with any ASC before your appointment date, if you have the Biometrics appointment and do it before the appointment date. many users were able to do it. Check H4 Biometrics Experiences
Scenario 2 : As mentioned above, you can try going to an ASC by walk-in before the date and give it. Many users had success, if one ASC does not do it, you can check with other one in the same area…usually users said, it works well in the afternoon for walk-ins…Give it a try and share your feedback in the thread for everyone benefit.
As far as travel goes, you need to be aware of situations of Travel Out of US with H4 Pending - Scenarios