Just so I completely understand this, 7805 fundamentally is a no-go b/c though it'll put out a regulated 5V and adding a resistor(lets say 125ohm) to it will bring it down to 3.3V, that 3.3V can and will change depending on the state of the module and the needed current of that particular state, thus changing the current going through the resistor, thus changing the resistance anywhere from 0-125, ultimately changing the 3.3V and either going too low or too high and frying my module.
It doesn't change the resistance. The resistance cannot change.
What it does is change the voltage that is dropped across the resistor.
Say you have a resistor of 125Ω, and a regulated 5V supply.
If the module draws 10mA then Ohms Law tells us that V=RxI, which is 125 x 0.01 which is 1.25, so the voltage after the resistor would be 5-1.25 = 3.75V.
If it draws 30mA, then the same formula: 125 * 0.03 = 3.75, so the voltage after the resistor at that point would be 5-3.75 = 1.25V. BT module cannot function.
If it only draws 5mA, then 125 * 0.005 = 0.625V, so the voltage after the resistor would be 5-0.625 = 4.375V and *bang* goes the BT module.
This is how ammeters work. A very small resistance is placed in the circuit where you want to find out the current, and the voltage dropped across that resistor is measured. Using Ohms Law the ammeter then calculates the current that must be flowing through the resistor.
These are some of the fundamentals that you really must get to grips with in order to do electronics.