Set option Editor | Strip trailing spaces to "Modified lines" value. Get the code with a line with trailing space:

public class A {

    private int untouchable1; // 1 space after: 

    private int untouchable2; // 1 space after: 

}

Go to the very end of the line with untouchable1. Press Enter. Save - the trailing space aftet the line is erased (line with untouchable2 was not changed - that's Ok). But I think from user's perspective the line was not changed. Spaces should probably not stripped in this case.