Can someone requests further modification after the revised deadline in an IEEE conference?
Contact the program chairs immediately. There is a moment in the publication process where changes are no longer possible, but this moment is not necessarily the deadline for revised papers.

Regarding the acceptability of such a request: Conference organizers are humans, too, so they will understand that people make errors and/or suboptimal choices. In addition, they might have an active interest in publishing the revised version: For example, a critical error that made it through the review process may reflect poorly on the conference and its organizers.