Resistors in a circuit--does it matter much?

Noob electronics question: Can I replace a 3Mohm 1/2 W resistor on a guitar pedal circuit with a 3.3Mohm resistor? Or even a 3Mohm 1/4W resistor? Will this cause the circuit to not work? Does it matter that much? I'm new to DIY electronics and can't find the answer with a google search.