What's this component and how could these screws affect it?
They are tuning screws. They alter the capacitance to ground of the circuit. They are either altering the centre frequency of filters or oscillators.

They will be set up in the factory once the box has been assembled. Once you've opened the box, there'll be no guarrantee you will get it back together with exactly the same position, so you may need to readjust the tuning screws to get back to correct performance.