It is cake to do. A couple screws come off, the old spring comes out, the new spring goes in. You won't be nervous about it if you actually see it in front of you. Changing the spring out is no more difficult than installing the joystick in the first place (in fact it is easier, much easier).
Note, you only put the heavy springs on these if you are putting long wico balltop handles on (which are a direct replacement for the handles on the P360, because the Happ p-360 is actually a member of the classic Wico family of sticks).
P360s are optical and thus basically silent in operation, no clicking to worry about. But remember I am talking about Perfect 360 sticks, the U360 is a sanwa stick isn't the same thing.