Is hamlet going to England as a prisoner or in the guise of royal representative?

In the play, Hamlet is actually sent to England under the false pretense of delivering King Claudius’ letter requesting England's king to execute him. However, Hamlet discovers and reads a plot in it to have him executed once he arrives , prompting him to change the content of the letter. Hamlet changes the text of the letter, effectively sending Rosencrantz and Guildenstern to their own deaths instead for what it originally planned for himself.