Flutter: Is it possible to format (bold, italicize, etc) with-in the string only before passing to the text widget?

You can use the flutter_html_view package for that.

String html = '<bold>Hello<bold> World';

new HtmlTextView(data: html);

If you just want different styles you can use a RichText widget with TextSpans like this.

new RichText( text: new TextSpan(text: 'Hello ', style: DefaultTextStyle.of(context).style, children:          
<TextSpan>[
new TextSpan(text: 'bold', style: new TextStyle(fontWeight: FontWeight.bold)), 
new TextSpan(text: ' world!'), 
], ), )