Brilliant solution. Almost - but only works for ArcGIS Pro.
ArcCatalog is ArcGIS 10.x and thus uses Python 2.7, where this doesn't work. Some digging came up with just
reload(your-module)
or there's another reload in module imp:
import imp
imp.reload(your-module)
which works for python 2 and 3.2-3.3 although I don't think there's Pro version that uses any of these Python versions.
Thanks for putting me on the right path!