diff --git a/FacadeFor3e.Tests/AttributeCollectionTests.cs b/FacadeFor3e.Tests/AttributeCollectionTests.cs
index 0c11105..d17d6d5 100644
--- a/FacadeFor3e.Tests/AttributeCollectionTests.cs
+++ b/FacadeFor3e.Tests/AttributeCollectionTests.cs
@@ -164,6 +164,30 @@ public void SetAnItem()
             ClassicAssert.AreEqual(n, coll[0]);
             }
 
+        [Test]
+        public void TestSetOrReplace()
+            {
+            var coll = new AttributeCollection
+                {
+                new NamedAttributeValue("boolean", new BoolAttribute(true)),
+                new NamedAttributeValue("integer", new IntAttribute(25)),
+                new NamedAttributeValue("guid", new GuidAttribute(Guid.NewGuid()))
+                };
+
+            var g = new NamedAttributeValue("guid", new BoolAttribute(true));
+            var i = new NamedAttributeValue("integer", new IntAttribute(25));
+            var t = new NamedAttributeValue("date", new DateTimeAttribute(DateTime.Now));
+
+            coll.AddOrReplace(g);
+            coll.AddOrReplace(i);
+            coll.AddOrReplace(t);
+
+            ClassicAssert.AreEqual(4, coll.Count);
+            ClassicAssert.AreEqual(g, coll["guid"]);
+            ClassicAssert.AreEqual(i, coll["integer"]);
+            ClassicAssert.AreEqual(t, coll["date"]);
+            }
+
         [Test]
         public void GetErrors()
             {
diff --git a/FacadeFor3e.Tests/FacadeFor3e.Tests.csproj b/FacadeFor3e.Tests/FacadeFor3e.Tests.csproj
index 6a9b454..27f1dca 100644
--- a/FacadeFor3e.Tests/FacadeFor3e.Tests.csproj
+++ b/FacadeFor3e.Tests/FacadeFor3e.Tests.csproj
@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
     <PackageReference Include="NUnit" Version="4.1.0" />
     <PackageReference Include="NLog" Version="5.3.2" />
   </ItemGroup>
diff --git a/FacadeFor3e/FacadeFor3e.csproj b/FacadeFor3e/FacadeFor3e.csproj
index 5f832f1..3737ee5 100644
--- a/FacadeFor3e/FacadeFor3e.csproj
+++ b/FacadeFor3e/FacadeFor3e.csproj
@@ -5,7 +5,7 @@
     <PackageId>FacadeFor3E</PackageId>
     <Authors>J Saffron Consulting</Authors>
     <Product>FacadeFor3E</Product>
-    <Version>4.0.0-rc3</Version>
+    <Version>4.0.0</Version>
     <Description>A library that makes integrating with Elite 3E a little easier</Description>
     <Copyright>Copyright © J Saffron Consulting Ltd 2014 - 2024</Copyright>
     <RepositoryUrl>https://github.com/JonSaffron/FacadeFor3e</RepositoryUrl>
diff --git a/FacadeFor3e/ProcessCommandBuilder/AttributeCollection.cs b/FacadeFor3e/ProcessCommandBuilder/AttributeCollection.cs
index 14e1ee3..77c7e8c 100644
--- a/FacadeFor3e/ProcessCommandBuilder/AttributeCollection.cs
+++ b/FacadeFor3e/ProcessCommandBuilder/AttributeCollection.cs
@@ -24,7 +24,6 @@ public NamedAttributeValue this[string name]
                 {
                 if (name == null)
                     throw new ArgumentNullException(nameof(name));
-                // ReSharper disable once PossibleNullReferenceException
                 var result = this.SingleOrDefault(a => a.Name.Equals(name, StringComparison.OrdinalIgnoreCase));
                 if (result == null)
                     throw new KeyNotFoundException("An attribute could not be found with the specified name.");
@@ -42,18 +41,39 @@ public bool TryGetValue(string name, [NotNullWhen(true)] out NamedAttributeValue
             {
             if (name == null)
                 throw new ArgumentNullException(nameof(name));
-            // ReSharper disable once PossibleNullReferenceException
             namedAttribute = this.SingleOrDefault(a => a.Name.Equals(name, StringComparison.OrdinalIgnoreCase));
             return namedAttribute != null;
             }
 
+        /// <summary>
+        /// Adds the specified attribute to the collection, or replaces it if an attribute with the same name is already present
+        /// </summary>
+        /// <param name="namedAttribute">The attribute to add or to replace</param>
+        /// <exception cref="ArgumentNullException">If <see cref="namedAttribute"/> is null</exception>
+        public void AddOrReplace(NamedAttributeValue namedAttribute)
+            {
+            if (namedAttribute == null) throw new ArgumentNullException(nameof(namedAttribute));
+            for (int i = 0; i < this.Count; i++)
+                {
+                var a = this[i];
+
+                if (a.Name.Equals(namedAttribute.Name, StringComparison.OrdinalIgnoreCase))
+                    {
+                    // ReSharper disable once RedundantBaseQualifier
+                    this.SetItem(i, namedAttribute);
+                    return;
+                    }
+                }
+
+            base.Add(namedAttribute);
+            }
+
         /// <inheritdoc />
         // ReSharper disable once AnnotationConflictInHierarchy
         protected override void InsertItem(int index, NamedAttributeValue item)
             {
             if (item == null)
                 throw new ArgumentNullException(nameof(item));
-            // ReSharper disable once PossibleNullReferenceException
             if (this.Any(a => a.Name.Equals(item.Name, StringComparison.OrdinalIgnoreCase)))
                 throw new ArgumentOutOfRangeException($"An attribute with the name {item.Name} has already been added.");
             base.InsertItem(index, item);
@@ -71,8 +91,6 @@ protected override void SetItem(int index, NamedAttributeValue item)
                     continue;
 
                 var a = this[i];
-                if (a == null)
-                    throw new InvalidOperationException();
                 if (a.Name.Equals(item.Name, StringComparison.OrdinalIgnoreCase))
                     throw new ArgumentOutOfRangeException($"An attribute with the name {item.Name} already exists.");
                 }
@@ -94,8 +112,6 @@ public bool Remove(string name)
                 {
                 var a = this[i];
 
-                if (a == null)
-                    throw new InvalidOperationException();
                 if (a.Name.Equals(name, StringComparison.OrdinalIgnoreCase))
                     {
                     // ReSharper disable once RedundantBaseQualifier
diff --git a/FacadeFor3e/ReleaseHistory.md b/FacadeFor3e/ReleaseHistory.md
index d3a365e..8df27f7 100644
--- a/FacadeFor3e/ReleaseHistory.md
+++ b/FacadeFor3e/ReleaseHistory.md
@@ -1,4 +1,8 @@
-4.0.0-rc3
+4.0.0
+-----
+Added AddOrReplace to AttributeCollection to serve a particular use case
+
+4.0.0-rc3
 ---------
 Change the ODataServiceResult.ErrorMesssages property to make it less brittle and enable it to cope with errors caused by rate limiting
 Updated the json deserialiser to be case-insensitive and to cache the options object