Whilst creating an iPhone application recently we had a need to be able to insert out own custom stylesheet and javascript, or jquery into certain web pages loaded within a UIWebView within the application.
We did it in the webViewDidFinishLoad section of the ViewController.m file:
[CSSWebView stringByEvaluatingJavaScriptFromString:@"var script = document.createElement('script');" "script.type = 'text/javascript';" "script.src = 'https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js';" "document.getElementsByTagName('head')[0].appendChild(script);"];
and
[CSSWebView stringByEvaluatingJavaScriptFromString:@"var link = document.createElement('link');" "link.type = 'text/css';" "link.rel = 'stylesheet';" "link.href = 'https://[your url goes in here]/style.css';" "document.getElementsByTagName('head')[0].appendChild(link);"];