@interface MyClass(CategoryA)

-(void)specificCategoryA;

@end


@interface MyClass(CategoryB)

-(void)specificCategoryB;

@end

@implementation MyClass

    -(void)utilityMethod {

      // choose one of the two...
      // -(void)specificCategoryB;
      // -(void)specificCategoryA;

    }

@end

#if some-constant-condition
  [mc specificCategoryA];
#else
  [mc specificCategoryB];
#endif

-(void)utilityMethod
{
    [super utilityMethod];
    // subclass specific code.
}

if ([object respondsToSelector:@selector(specificCategoryA)]) {
   [object specificCategoryA];
}
else if ([object respondsToSelector:@selector(specificCategoryB)]) {
   [object specificCategoryB];
}