Enable customer order number field in Completed state

I would advise taking a look at the solution below on how to do it.

In short, I believe you require:

1. An extended workflow with editable fields under required state with Disabled = unticked
2. Code to enable the field.

Here is a sample for our SOOrderEntry which has been customised to enable editing of price and ext price. This is to amend SOLine though, so Order Number may require some tweaking.

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using PX.Common;
using PX.Data;
using PX.Objects.AP;
using PX.Objects.AR;
using PX.Objects.CA;
using PX.Objects.CM;
using PX.Objects.CR;
using PX.Objects.CS;
using PX.Objects.DR;
using PX.Objects.EP;
using PX.Objects.GL;
using PX.Objects.IN;
using PX.Objects.PM;
using PX.Objects.PO;
using PX.Objects.TX;
using POLine = PX.Objects.PO.POLine;
using POOrder = PX.Objects.PO.POOrder;
using System.Threading.Tasks;
using PX.CarrierService;
using CRLocation = PX.Objects.CR.Standalone.Location;
using PX.Objects.AR.CCPaymentProcessing;
using PX.Objects.AR.CCPaymentProcessing.Common;
using PX.Objects.AR.CCPaymentProcessing.Helpers;
using PX.Objects.AR.CCPaymentProcessing.Interfaces;
using ARRegisterAlias = PX.Objects.AR.Standalone.ARRegisterAlias;
using PX.Objects.AR.MigrationMode;
using PX.Objects.Common;
using PX.Objects.Common.Discount;
using PX.Objects.Common.Extensions;
using PX.Objects.IN.Overrides.INDocumentRelease;
using PX.CS.Contracts.Interfaces;
using Message = PX.CarrierService.Message;
using PX.TaxProvider;
using PX.Data.DependencyInjection;
using PX.Data.WorkflowAPI;
using PX.LicensePolicy;
using PX.Objects.Extensions.PaymentTransaction;
using PX.Objects.SO.GraphExtensions.CarrierRates;
using PX.Objects.SO.GraphExtensions.SOOrderEntryExt;
using PX.Objects.SO.Attributes;
using PX.Objects.Common.Attributes;
using PX.Objects.Common.Bql;
using OrderActions = PX.Objects.SO.SOOrderEntryActionsAttribute;
using PX.Objects.SO.DAC.Projections;
using PX.Data.BQL.Fluent;
using PX.Objects;
using PX.Objects.SO;

namespace PX.Objects.SO
{
  public class SOOrderEntry_Extension : PXGraphExtension<PX.Objects.SO.SOOrderEntry>
  {
    #region Event Handlers
        protected virtual void SOLine_RowSelected(PXCache cache, PXRowSelectedEventArgs e, PXRowSelected InvokeBaseHandler)
        {
            InvokeBaseHandler?.Invoke(cache, e);
            SOLine row = e.Row as SOLine;
            if (row != null)
            {
                Base.Document.Cache.AllowUpdate = true;
                PXUIFieldAttribute.SetEnabled<SOLine.curyUnitPrice>(cache, row, true);
                PXUIFieldAttribute.SetEnabled<SOLine.curyExtPrice>(cache, row, true);
                
            }
        }
    #endregion
  }
}