How to change a data from a Anonymous query on EntityFramework

I'm using Entity Framework and I have a Table Users, and a Row with a data that needs to be Decrypted, the problem is when I make a query to make a list of these users I can't directly Decrypt because is a Anonymous type..

 var query = context.Users.Where(x => x.Id == id).Select(x => new
 {
    x.Id,
    x.FirstName,
    x.LastName,
    x.UCP
 });
 response = Request.CreateResponse(HttpStatusCode.OK, query.ToList());

So how to change the data from UCP to a decrypted Data, I'm not asking how to Decrypt but how to Change!