how to switch between normal signal and modified signal with analog intput signals arduino?
Are you looking for a bypass switch? This is very common in guitar circuits using a DPDT switch.



If you also want to switch power, you can use this method and use the other pole as a power switch, or you can just use the first method and a DP3T switch, which is a little harder to come by.



Picture credit http://screaminfx.com/tech/what-is-true-bypass-guitar-pedal.htm