When i’m trying to change a variable value i have to make this huge node which has default value for anything, how can i change only one setting without override them all ?
You need to deselect them all in the node’s details and then select only the one you need. Or, you can find one over here:
Copy and paste that text into your BP and you’ll get a clean node with nothing enabled.
If you look closely you can see i’v posted this thread XD
But even when they are not selected they are still effecting the values.
Haha, sorry about that. 
Well how are you setting the blueprint exactly? I was able to change only depth of field settings of a camera this way. Is it a camera or a PP volume, btw?
PP Volume. If you use default values it doesn’t matter but if have you custom settings for your scene this is problematic.