so to answer my own question:

if you create a shelf tool with the following python script:

if hou.ui.updateMode() == hou.updateMode.AutoUpdate:
    hou.ui.setUpdateMode(hou.updateMode.Manual)
else:
    hou.ui.setUpdateMode(hou.updateMode.AutoUpdate)

you can easily assign a hotkey by ctrl - alt - shift clicking on it.

I hope somebody finds this as useful as I do.

By: Georg Kaltenbrunner [ Editor ]