I just posted a radar to suggest an enhancement to the way ClockKit currently handles the placeholder templates for the Apple Watch complications.
Here is the text I submitted:
I am developing a watch app with complications that can be customised by the user. It would be nice for users to see a placeholder according to the data and format they customised. Currently templates are loaded only once at app install. A great improvement would be an API call from the iPhone companion app to request reloading of all (or some) of the complication templates.