I understand what you are seeking....
However, Inkscape is not a 3D application.
What you have are flat, non-dimensional, objects. i.e. just 3 rectangles with sides at various angles, that's all.
Any apparent dimensioning due to the isometric angles is just appearance, not real dimensional projections. As far as I'm aware, Inkscape doesn't create real 3D projections, including isometric projections. You need a 3D application for that.
If you wish to change the view angle, you must redraw at the angle you want.
Inkscape, like all 2D applications, understands X and Y on flat, perpendicular planes... meaning...
Inkscape has no clue what Z is.
In short, you are seeking 3D functionality in a non-3D application.