iOS/Objective-C "if" best practice
First of all, using the tag to distinguish between views is almost everytime (there are exceptions) a bad idea. It's much cleaner to use your own variable (pointers to view, BOOL flags).

10 is a magic number. What does it mean? Use a constant.

Use methods. Four levels of if are terrible. Extract the code into methods.

if ([self isVerticalScrollingDisabled] || [self isHorizontalScrollingDisabled]) {
    return;
}

[super setAlpha:alpha];


By the way, changing the behavior of a method in a subclass (the method sets alpha only if some conditions are valid) is smelly from architecture point of view. Declaring a special method, e.g. setAlphaIfScrollingEnabled: would be better.