Whenever I use group SOP that would be named as "$OS" , therefore doing this manually would be a time wasting. This would be small trick for onCreated.py. file. Basically the user operator preset named "default" will be called whenever nodes is being created. For example
## Load User Named "default" automatically
#Defintion
def default():
node = kwargs["node"]
path = node.path()
op_path = path
preset_name = 'default'
cmd = 'oppresetload %s "%s"' % (op_path, preset_name)
hou.hscript(cmd)
#Invoke
default()