Can I use my still valid H4 EAD after my H1 to H4 COS is approved?

  It does not appear that you would be able to use the H-4 EAD that you previously had in the situation that you describe. That is because you are presently under H-1B status and would not have H-4 status again until the application is approved. That would present a mismatch situation that would not be allowed of an H-4 EAD while under H-1B status. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.