When they are not in the church etc or when they go on holiday they can definitely wear other clothes
I was schooled in a parochial school. All the teachers were nuns in various forms and colors of habits. When I read the question I immediately began to visualize a few those nuns in jeans and I haven't stopped laughing for the last 10 minutes. Thank you.
I am sure others who had the "nun experience" will agree. In some cases the visuion would be horrifying.