InstanceDefinitionIsDeleted Property

using Rhino;
using Rhino.Input;
using Rhino.Commands;

namespace examples_cs
{
  public class RenameBlockCommand : Command
  {
    public override string EnglishName { get { return "csRenameBlock"; } }

    protected override Result RunCommand(RhinoDoc doc, RunMode mode)
    {
      // Get the name of the insance definition to rename
      var instance_definition_name = "";
      var rc = RhinoGet.GetString("Name of block to rename", true, ref instance_definition_name);
      if (rc != Result.Success)
        return rc;
      if (string.IsNullOrWhiteSpace(instance_definition_name))
        return Result.Nothing;

      // Verify instance definition exists
      var instance_definition = doc.InstanceDefinitions.Find(instance_definition_name, true);
      if (instance_definition == null) {
        RhinoApp.WriteLine("Block \"{0}\" not found.", instance_definition_name);
        return Result.Nothing;
      }

      // Verify instance definition is rename-able
      if (instance_definition.IsDeleted || instance_definition.IsReference) {
        RhinoApp.WriteLine("Unable to rename block \"{0}\".", instance_definition_name);
        return Result.Nothing;
      }

      // Get the new instance definition name
      string instance_definition_new_name = "";
      rc = RhinoGet.GetString("Name of block to rename", true, ref instance_definition_new_name);
      if (rc != Result.Success)
        return rc;
      if (string.IsNullOrWhiteSpace(instance_definition_new_name))
        return Result.Nothing;

      // Verify the new instance definition name is not already in use
      var existing_instance_definition = doc.InstanceDefinitions.Find(instance_definition_new_name, true);
      if (existing_instance_definition != null && !existing_instance_definition.IsDeleted) {
        RhinoApp.WriteLine("Block \"{0}\" already exists.", existing_instance_definition);
        return Result.Nothing;
      }

      // change the block name
      if (!doc.InstanceDefinitions.Modify(instance_definition.Index, instance_definition_new_name, instance_definition.Description, true)) {
        RhinoApp.WriteLine("Could not rename {0} to {1}", instance_definition.Name, instance_definition_new_name);
        return Result.Failure;
      }

      return Result.Success;
    }
  }
}

Imports Rhino
Imports Rhino.Commands

Namespace examples_vb
  Public Class RenameBlockCommand
    Inherits Command
    Public Overrides ReadOnly Property EnglishName() As String
      Get
        Return "vbRenameInstanceDefinition"
      End Get
    End Property

    Protected Overrides Function RunCommand(doc As RhinoDoc, mode As RunMode) As Result
      ' Get the name of the insance definition to rename
      Dim instanceDefinitionName As String = ""
      Dim rc = Rhino.Input.RhinoGet.GetString("Name of block to rename", True, instanceDefinitionName)
      If rc <> Result.Success Then
        Return rc
      End If
      If [String].IsNullOrWhiteSpace(instanceDefinitionName) Then
        Return Result.[Nothing]
      End If

      ' Verify instance definition exists
      Dim instanceDefinition = doc.InstanceDefinitions.Find(instanceDefinitionName, True)
      If instanceDefinition Is Nothing Then
        RhinoApp.WriteLine([String].Format("Block ""{0}"" not found.", instanceDefinitionName))
        Return Result.[Nothing]
      End If

      ' Verify instance definition is rename-able
      If instanceDefinition.IsDeleted OrElse instanceDefinition.IsReference Then
        RhinoApp.WriteLine([String].Format("Unable to rename block ""{0}"".", instanceDefinitionName))
        Return Result.[Nothing]
      End If

      ' Get the new instance definition name
      Dim instanceDefinitionNewName As String = ""
      rc = Rhino.Input.RhinoGet.GetString("Name of block to rename", True, instanceDefinitionNewName)
      If rc <> Result.Success Then
        Return rc
      End If
      If [String].IsNullOrWhiteSpace(instanceDefinitionNewName) Then
        Return Result.[Nothing]
      End If

      ' Verify the new instance definition name is not already in use
      Dim existingInstanceDefinition = doc.InstanceDefinitions.Find(instanceDefinitionNewName, True)
      If existingInstanceDefinition IsNot Nothing AndAlso Not existingInstanceDefinition.IsDeleted Then
        RhinoApp.WriteLine([String].Format("Block ""{0}"" already exists.", existingInstanceDefinition))
        Return Result.[Nothing]
      End If

      ' change the block name
      If Not doc.InstanceDefinitions.Modify(instanceDefinition.Index, instanceDefinitionNewName, instanceDefinition.Description, True) Then
        RhinoApp.WriteLine([String].Format("Could not rename {0} to {1}", instanceDefinition.Name, instanceDefinitionNewName))
        Return Result.Failure
      End If

      Return Result.Success
    End Function
  End Class
End Namespace

import rhinoscriptsyntax as rs
from scriptcontext import doc

def Rename():
    blockName = rs.GetString("block to rename")
    instanceDefinition = doc.InstanceDefinitions.Find(blockName, True)
    if not instanceDefinition: 
        print "{0} block does not exist".format(blockName)
        return

    newName = rs.GetString("new name")
    instanceDefinition = doc.InstanceDefinitions.Find(newName, True)
    if instanceDefinition: 
        print "the name '{0}' is already taken by another block".format(newName)
        return

    rs.RenameBlock(blockName, newName)

if __name__ == "__main__":
    Rename()