Can one say
a. I responded to their letter as an official document, similar to the ones sent to me by the Ministry of Education.
b. I reacted to his behavior as a narcissistic outburst, similar to his ravings against his father.
Are they grammatical?
This is the place to post questions and discussions on usage and style. The members of the Wordwizard Clubhouse will also often be able to help you to formulate that difficult letter.
End of topic.