Now here is my question:
Is it possible to grab the content of a figure and 'displace' it in a subplot of the same figure, to give room for a knew plot - even if the original content is complex (i.e. an image + a colorbar + an histogram, for example).
I am not sure I'm clear here, so I can try to rephrase if needed.
I am not sure if you are trying to move objects from one axes to another or merely reposition an existing axes to make room for a new one.
Both are possible, but the latter is easy. Each axes has [left, bottom, width, height] rectangle in (0,1) figure coordinates that you can adjust at any time. See for example the subplots_adjust tool on the navigation toolbar next to the save icon
colorbars are a little tricky, because there you are needing to reposition *two* axes, one for the image, and one for the colorbar itself. You can do this manually, but you probably want to look at JJ's gridspec and axes_grid tools for laying out groups of axes: