Hi Peter,

Below is an example of the Saving event and setting a member property value:

using Umbraco.Core;
using Umbraco.Core.Events;
using Umbraco.Core.Models;
using Umbraco.Core.Services;

namespace MyApplication.Events
{
    public class MemberSavingEvent : ApplicationEventHandler
    {
        public MemberSavingEvent() 
        {
            MemberService.Saving += MemberServiceOnSaving;
        }

        private static void MemberServiceOnSaving(IMemberService sender, SaveEventArgs saveEventArgs)
        {
            foreach (var member in saveEventArgs.SavedEntities)
            {
                member.SetValue("propertyAlias", "value");
            }
        }
    }
}

Thanks,
Dan.