How to Change a z3c.form Date Widget with javascript

Sorry if this answer is stupid ( I never tried this):
I was thinking on modifying the html as I thought the js script read it when you 'clicked the button':

So, my idea was to only change
input class="pat-pickadate" value="maybesomething" etc />

input class="pat-pickadate" value="2030-01-01 01:01" etc />