If an applicant is awarded an EN grant this year, and later realizes the project is going to require a completely different component for the project to be successful (but this component was not in the original application), could we apply for a grant focused on that additional component the following year?

Applicants can definitely apply in consecutive years; however, work being proposed in a follow-on grant should not duplicate work carried out during the previous grants.  Applicants applying for EN grants in consecutive years are often targeting projects areas (e.g., air, water, waste, etc.), separate and distinct from the original grant award. It likely makes more sense in this example for the grantee to do a project change request and  budget modification with their Project Officer (PO), to reflect the purchase and/or implementation of the new component in the original project.