using DevExpress.Utils.Design;
//..

[ToolboxSvgImage("WinFormsApp_CustomNumericLabel.NumericLabel.svg, WinFormsApp_CustomNumericLabel")]
public class NumericLabel : XRLabel { ... }

Imports DevExpress.Utils.Design
'..

<ToolboxSvgImage("WinFormsApp_CustomNumericLabel.NumericLabel.svg, WinFormsApp_CustomNumericLabel")>
Public Class NumericLabel
    Inherits XRLabel

    Private ...}

using DevExpress.Utils.Design;
using System.Drawing;
//...

namespace WinFormsApp_CustomNumericLabel {
    [ToolboxBitmap(typeof(NumericLabel), "NumericLabel.png")]
    [ToolboxBitmap24Attribute("WinFormsApp_CustomNumericLabel.NumericLabel24x24.png, WinFormsApp_CustomNumericLabel")]
    public class NumericLabel : XRLabel { ... }
}

Imports DevExpress.Utils.Design
Imports System.Drawing
'...

Namespace WinFormsApp_CustomNumericLabel
    <ToolboxBitmap(GetType(NumericLabel), "NumericLabel.png"), ToolboxBitmap24Attribute("WinFormsApp_CustomNumericLabel.NumericLabel2.png, WinFormsApp_CustomNumericLabel")>
    Public Class NumericLabel
        Inherits XRLabel

        Private ...}
    End Class

using DevExpress.XtraReports.UI;
using DevExpress.XtraReports.UserDesigner;
using System;
using System.Drawing.Design;
using System.Windows.Forms;

// ...
void ShowDesignerWithCustomControl()
{
    // Creates a Design Tool instance with the specified report instance.
    ReportDesignTool designTool = new ReportDesignTool(new XtraReport1());
    IDesignForm designForm = designTool.DesignForm;
    designForm.DesignMdiController.DesignPanelLoaded += DesignMdiController_DesignPanelLoaded;
    designTool.ShowDesignerDialog();
}

void DesignMdiController_DesignPanelLoaded(object sender, DesignerLoadedEventArgs e) {
    IToolboxService toolboxService =
        (IToolboxService)e.DesignerHost.GetService(typeof(IToolboxService));
    // Removes the XRLabel toolbox item.
    toolboxService.RemoveToolboxItem(
        GetToolBoxControl(toolboxService, "DevExpress.XtraReports.UI.XRLabel"));
    // Creates a new toolbox item for the custom control.
    ToolboxItem numericLabelItem = new ToolboxItem(typeof(NumericLabel))
    {
        // Specifies the name in the toolbox.
        DisplayName = "Numeric Label"
    };
    // Adds the new control to the toolbox.
    toolboxService.AddToolboxItem(numericLabelItem);
}

ToolboxItem GetToolBoxControl(IToolboxService toolboxService, string name) {
    foreach (ToolboxItem item in toolboxService.GetToolboxItems()) {
        if (item.TypeName == name) { return item; };
    }
    return null;
}

Imports DevExpress.XtraReports.UI
Imports DevExpress.XtraReports.UserDesigner
Imports System
Imports System.Drawing.Design
Imports System.Windows.Forms
' ...
        Private Sub ShowDesignerWithCustomControl()
            ' Creates a Design Tool instance with the specified report instance.
            Dim designTool As New ReportDesignTool(New XtraReport1())
            Dim designForm As IDesignForm = designTool.DesignForm
            AddHandler designForm.DesignMdiController.DesignPanelLoaded, AddressOf DesignMdiController_DesignPanelLoaded
            designTool.ShowDesigner()
        End Sub

        Private Sub DesignMdiController_DesignPanelLoaded(ByVal sender As Object, ByVal e As DesignerLoadedEventArgs)
            Dim toolboxService As IToolboxService = DirectCast(e.DesignerHost.GetService(GetType(IToolboxService)), IToolboxService)
            ' Removes the XRLabel toolbox item.
            toolboxService.RemoveToolboxItem(GetToolBoxControl(toolboxService, "DevExpress.XtraReports.UI.XRLabel"))
            ' Creates a new toolbox item for the custom control.
            Dim numericLabelItem As New ToolboxItem(GetType(NumericLabel)) With {.DisplayName = "Numeric Label"}
            ' Adds the new control to the toolbox.
            toolboxService.AddToolboxItem(numericLabelItem)
        End Sub

        Private Function GetToolBoxControl(ByVal toolboxService As IToolboxService, ByVal name As String) As ToolboxItem
            For Each item As ToolboxItem In toolboxService.GetToolboxItems()
                If item.TypeName = name Then
                    Return item
                End If
            Next item
            Return Nothing
        End Function