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...

[![enter image description here][1]][1]


Inkscape has *no clue* what Z is.

In short, you are seeking 3D functionality in a **non-3D** application.


  [1]: https://i.sstatic.net/LHeqr.png