I am afraid that indeed such manipulations are feasible at the client's side, however, we cannot grantee and prevent this. Many many different operations may be performed with the developer tool at the client - from changes in the layout to enabling/disabling specific elements from the DOM.
This is why, this scenario falls out of the support scope. You can ensure however that the proper business logic is kept in your project at server-side, by implementing the needed validations.
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