Is it possible to edit html file by clicking a few buttons through variables and functions in the app?
Maybe this can help you :
In a nutshell - yes. You can put the HTML code into a Text Box for editing and display the result in a Web View. A lot depends on your HTML + CSS skills and if you are talking variables and functions, javascript too. However, a Smartphone is far from the best environment for Web page editing. Perhaps you could give more details concerning the goal of your App.
Please note that the data uri method for the webview is currently broken. e.g.
data: text/html, <html>Hello World</html>
will crash your app, so you will need to use html files and edit them.