yes, once you use EAD, your H1 will be invalid. However, you can resume H4 (affiliated to your LG's H1) if 485 is denied. Just simply file 539 and go outside for an H4 stamp.
Now you plan to switch to H4 then use EAD to work. This is not necessary and not pratical as once you use EAD, H4 will be also invalid.