You could create a generic function for combining functions, it might look something like this:

def combine_funcs(*funcs):
    def combined_func(*args, **kwargs):
        for f in funcs:
            f(*args, **kwargs)
    return combined_func

Then you could create your button like this:

self.testButton = Button(self, text = "test", 
                         command = combine_funcs(func1, func2))

Make a new function that calls both:

def o_and_t():
    o()
    t()
button = Button(admin, text='Press', command=o_and_t)

Alternatively, you can use this fun little function:

def sequence(*functions):
    def func(*args, **kwargs):
        return_value = None
        for function in functions:
            return_value = function(*args, **kwargs)
        return return_value
    return func

Then you can use it like this:

button = Button(admin, text='Press', command=sequence(o, t))

Instead of self.restartExternal() and restartWindow.destroy you could do [self.restartExternal(), restartWindow.destroy()]. This way, it will call restartWindow.destroy() whatever self.restartExternal() returns, whereas how it is, if self.restartExternal() returns False, Python doesn't even check to see if restartWindow.destroy is True or False. Besides that, restartWindow.destroy isn't even called in yours, because you left out the parentheses.

You can have your commend1() to call commend2() like this :

def commend1():
  print "hi"
  commend2()

def commend2():
  print "hello"

#TKinter
button = Button(root, command= commend1)