Webviewのnavigator.userAgentを独自のユーザーエージェントにする方法と、その他諸注意（Googel Analytics etc..） ref: http://qiita.com/unamu/items/078ca02c0e3444247ac4

file0.m

UIWebView *webView = [[UIWebView alloc] initWithFrame:CGRectZero];
NSString *userAgent = [webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];
NSString *customUserAgent = [userAgent stringByAppendingString:@" HOGEHOGE"];

file1.m

NSDictionary *dictionary = [[NSDictionary alloc] initWithObjectsAndKeys:customUserAgent , @"UserAgent", nil];
[[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];