Is it possible to modify the data or functionality using browser developer toolbox?

[Suggy]

Is it possible to modify the data or functionality using browser developer toolbox?

Ex 1 - On Incident form, I have short description as mandatory. Using browser developer tool option, can I make it Not mandatory?

Ex 2 - Using browser developer toolbox, can I manipulate form data? Ex - state field is read only. Can I change the value to something else?

PS - I tried doing so, but couldn't do it, but my colleague says he can do so.

[Suggy]

@Ravi Gaurav I have written onload client script on incident form and made description as mandatory field. Can anyone bypass that is my question? ie using browser developer tools, make it non-mandatory and submit the form without filling anything in description?