The microphone API is here:
I haven't used it, but I guess you could override the default name by inserting a code component below the microphone component and in its
Begin routine tab, put something like:
mic_1.setFile('Some alternative name.wav')
Of course, you'll want to make this filename vary from trial to trial so that it doesn't just overwrite the previous one, but you'd need to decide on a naming convention (e.g. include subject code plus trial number).
I don't know if this would break any other functionality.