In there an app (preferably Android) that can take a audio recording (music, voice, etc.) and change the frequency to above or below human hearing (infrasonic and ultrasonic) and vice versa. I want to explore the possibilities of what I can do with it. I played with a few frequency generators but it's limited.
TL:DR You will not be able to do this in any meaningful way on a phone.
I'm not sure what you mean by 'modulation recorded audio' [unless you're referring to PCM, pulse-code modulation] but you can change frequencies most simply by changing sampling rate for playback - in effect speed it up or slow it down.
Alternatively, there are algorithms that can change pitch independantly of speed. Even the simplistic Audacity has a pitch-shift module.
Your main problems in doing this are going to be
Pitch-shifting by extreme amounts distorts the signal quite badly, introducing unwanted artefacts.
You probably lack the equipment to actually play back any audio outside the normal human hearing spectrum… not that you could hear it if it did. You will certainly never achieve this kind of playback on a phone; not even on a home hifi or HTPC. It requires expensive, specialist equipment.
Apart from playback, you also lack the equipment to record anything outside the human hearing spectrum. See How can I record frequencies from 0.1 to 20 Hz? for the low end. You will hit comparable issues at the high end.