AlwaysUpdate attribute for Entity Framework Code First POCO
Instead of checking .Count() &gt; 0 which needs to iterate over the IEnumerable you can just use .Any() which only checks if at least one item is contained in the IEnumerable  
you should extract the result of typeof(AlwaysUpdateAttribute) to a variable.  

Type desiredType = typeof(AlwaysUpdateAttribute);

you can restrict the outer loop by adding the "continue condition" to the Where() method. For readability we will do this outside of the loop  

changeSet = changeSet.Where( c=&gt;   
            c.State == System.Data.EntityState.Modified 
              &amp;&amp; !(entry.State == System.Data.EntityState.Added   
              || entry.State == System.Data.EntityState.Unchanged)  
             );  

you shouldn't shorten any variable names -> prop should be propertyName


Refactoring  

Implementing all above will lead to  

public override int SaveChanges()
{
    var changeSet = ChangeTracker.Entries();
    if (changeSet != null)
    {
        changeSet = changeSet.Where( c=&gt;   
                 c.State == System.Data.EntityState.Modified 
                  &amp;&amp; !(entry.State == System.Data.EntityState.Added   
                  || entry.State == System.Data.EntityState.Unchanged)  
                  );   

        Type desiredType = typeof(AlwaysUpdateAttribute);

        foreach (var entry in changeSet)
        {
            foreach (var propertyName in entry.Entity.GetType().GetProperties().Where(p =&gt; p.GetCustomAttributes(desiredType , true).Any()).Select( p =&gt; p.Name ))
            {
                // Try catch removes the errors for detached and unchanged items
                try
                {
                    entry.Property(propertyName).IsModified = true;
                }
                catch { }
            }
        }
    }
    return base.SaveChanges();
}


    foreach (var entry in changeSet) 
    {
        foreach (var prop in entry.Entity.GetType().GetProperties().Where(p =&gt; p.GetCustomAttributes(desiredType , true).Any()).Select( p =&gt; p.Name ))
        {
            // Try catch removes the errors for detached and unchanged items
            try
            {
                entry.Property(prop).IsModified = true;
            }
            catch { }
        }