In general, you can do this if you were making programmatic UIs. However, GUIDE sets its own defaults that can't be changed to my knowledge.
With a regular figure:
hFig = figure;
set(hFig,'Defaultuicontrolunits','pixels')
set(hFig,'Defaultaxesunits','pixels')
set(hFig,'Defaultuipanelunits','pixels')
I would recommend IA's approach. You can also right click a graphics component in GUIDE to make a copy of it. That way you change the properties once, right click and drag to get an identical object.