The word transgender never needs the extraneous "ed" at the end of the word. In fact, such a construction is grammatically incorrect. Only verbs can be transformed into participles by adding "-ed" to the end of the word, and transgender is an adjective, not a verb.
Transgender should be used as an adjective, not as a noun. Do not say, 'Tony is a transgender,' or 'The parade included many transgenders.' Instead say, 'Tony is a transgender person,' or 'The parade included many transgender people.