When you export with "render text as images," of course, those anchor points get mapped with their co-ordinates (which is what you referenced above). So it may be possible to change those, it would be difficult and could end up breaking the navigation. Exporting with text rendered as HTML text could also end up breaking the navigation. You might have better luck with this option, but you introduce the risk of the text not appearing the same as your layout. Rendering as images gives you the greatest fidelity between your InDesign layout and the HTML output.