private void richEditControl1_HyperlinkFormShowing(object sender,HyperlinkFormShowingEventArgs e)
{
    using (MyHyperlinkForm form = new MyHyperlinkForm(e.ControllerParameters))
    {
        e.DialogResult = form.ShowDialog();
        e.Handled = true;
    }
}

Private Sub richEditControl1_HyperlinkFormShowing(ByVal sender As Object, ByVal e As HyperlinkFormShowingEventArgs)
    Using form As New MyHyperlinkForm(e.ControllerParameters)
        e.DialogResult = form.ShowDialog()
        e.Handled = True
    End Using
End Sub

using System;
using DevExpress.XtraRichEdit.Forms;

namespace CustomDialogs {
    class MyHyperlinkForm : HyperlinkForm {
        public MyHyperlinkForm(HyperlinkFormControllerParameters controllerParameters)
            : base(controllerParameters)
        {
            btnEditAddress.EditValueChanged += new EventHandler(btnEditAddress_EditValueChanged);
            btnEditAddress.LostFocus += new EventHandler(btnEditAddress_LostFocus);
        }

        void btnEditAddress_LostFocus(object sender, EventArgs e) {
            this.btnEditAddress.Text = Controller.NavigateUri;
        }

        void btnEditAddress_EditValueChanged(object sender, EventArgs e) {
            Controller.NavigateUri = ValidateUrl(btnEditAddress.Text);
            this.btnOk.Enabled = true;
        }

        private string ValidateUrl(string p) {
            string s = p.Replace("devexpres.com", "devexpress.com");
            return s;
        }

    }
}

Imports Microsoft.VisualBasic
Imports System
Imports DevExpress.XtraRichEdit.Forms

Namespace CustomDialogs
    Friend Class MyHyperlinkForm
        Inherits HyperlinkForm
        Public Sub New(ByVal controllerParameters As HyperlinkFormControllerParameters)
            MyBase.New(controllerParameters)
            AddHandler btnEditAddress.EditValueChanged, AddressOf btnEditAddress_EditValueChanged
            AddHandler btnEditAddress.LostFocus, AddressOf btnEditAddress_LostFocus
        End Sub

        Private Sub btnEditAddress_LostFocus(ByVal sender As Object, ByVal e As EventArgs)
            Me.btnEditAddress.Text = Controller.NavigateUri
        End Sub

        Private Sub btnEditAddress_EditValueChanged(ByVal sender As Object, ByVal e As EventArgs)
            Controller.NavigateUri = ValidateUrl(btnEditAddress.Text)
            Me.btnOk.Enabled = Not String.IsNullOrEmpty(Me.btnEditAddress.Text)
        End Sub

        Private Function ValidateUrl(ByVal p As String) As String
            Dim s As String = p.Replace("devexpres.com", "devexpress.com")
            Return s
        End Function

    End Class
End Namespace