1- what is the use of modify form submission for GET, POST, GET&POST, None ?
2- The use of changing user agent in option profile ?
Assuming this is a web application many web server can be restricted to allow only certain types of methods such as POST, GET. A good security practice would be to remove or limit the methods the web server accepts. So if your application never needs anything with say a DELETE then you would remove that via configuration so the server does not accept such a request. That being said GET & POST operate slightly different and beyond what I will go into here. I suggest you do some reading online to get more details on both just to understand how they can impact an application.
Now the user agents the basically the browser name. Many application will use the user agent to try and determine what type of browser and/or platform you are on. The User Agent string from Chrome on a windows box is different that what Chrome send from a mobile device. Many platforms detect this difference and will give different content for a different user agent. I have exploited systems many times by just sending an unexpected user agent such as forcing my desktop browser to look like a mobile device.
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