Change SDWebImage cache directory

SDImageCache.m

@implementation SDImageCache 
...
+ (void)changeDefaultCacheDiskToDocument
{
    Method origMethod = class_getInstanceMethod(self, @selector(initWithNamespace:));
    Method replaceMethod = class_getInstanceMethod(self, @selector(initWithNamespaceInDocument:));
    if (origMethod && replaceMethod) {
        method_exchangeImplementations(origMethod, replaceMethod);
    }
}

- (id)initWithNamespaceInDocument:(NSString *)ns {
    if ((self = [super init])) {
        NSString *fullNamespace = [@"image." stringByAppendingString:ns];
        
        // Create IO serial queue
        _ioQueue = dispatch_queue_create("com.hackemist.SDWebImageCache", DISPATCH_QUEUE_SERIAL);
        
        // Init default values
        _maxCacheAge = kDefaultCacheMaxCacheAge;
        
        // Init the memory cache
        _memCache = [[NSCache alloc] init];
        _memCache.name = fullNamespace;
        
        // Init the disk cache
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        _diskCachePath = [paths[0] stringByAppendingPathComponent:fullNamespace];
        
        dispatch_sync(_ioQueue, ^{
            _fileManager = [NSFileManager new];
        });
        
#if TARGET_OS_IPHONE
        // Subscribe to app events
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(clearMemory) name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(cleanDisk) name:UIApplicationWillTerminateNotification object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(backgroundCleanDisk) name:UIApplicationDidEnterBackgroundNotification object:nil];
#endif
    }
    
    return self;
}
...
@end
    
    
/***********Usage:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
	[SDImageCache changeDefaultCacheDiskToDocument];
    ...
}
*****************/

你好，麻烦问下你这个更改默认cachePath的方法，类名称和SDImageCache一样，那如何调用来将原来的方法给覆盖掉呢？
还是说你直接改的SDImageCache类呢？