Q: If a Deacon is attending Mass in choir and is asked to read the daily readings or distribute Holy communion. Should he do this in his street clothes or does he need to vest and serve the Mass? I also assume a polite decline is an option.
A: Here’s a previous post: https://paulturner.org/choir-dress-for-deacon/
In my view, and without any documentation, a deacon who attends Mass without vestments could proclaim a reading or distribute communion.
But the ideal is that he vest and serve as a deacon. Every Mass has a role for a deacon, even a daily Mass. A priest presiding without a deacon is covering two roles.