W-4 is for tax withholding and is not sent to IRS. I-9 is the employment eligibility verification form. The information from EAD will be recorded there. While this is also not sent to anywhere, a use of EAD may invalidate other VISA status you are holding. No one is watching you using EAD and stamping “void” on your papers, but you will likely get into a trouble in the future, if your GC application gets rejected. To be in the safe side, try to maintain and use the H1B until your case gets approved.