Did you edit the file going to the Project tab, "Resources" then edit against "EndDialog.aspx"?
And just update the Text="My Text"
<div style="text-align:left;margin-top:10em">
<h5><asp:Localize runat="server" meta:resourcekey="lblReplaceNote" Text="My Text" /></h5>
<div>
Then once published if you check the file in Release does it doesn't reflect your changes?
[InstallDrive]:\Program Files\Symantec\Workflow\WorkflowDeploy\Release\{PROJECTNAME}\EndDialog.aspx
The issue here is it uses a Resource file with localisations in.
If you open
[InstallDrive]:\Program Files\Symantec\Workflow\WorkflowDeploy\Release\POC_End_WEB\App_LocalResources\EndDialog.aspx.resx
and look for "lblReplaceNote"
<data name="lblReplaceNote.Text" xml:space="preserve">
<value>* You can edit or replace this file in the project directory.</value>
</data>
And update it
<data name="lblReplaceNote.Text" xml:space="preserve">
<value>My Text</value>
</data>
The message will then be reflected.
I don't tend to let the WF show this page, I create another Form using a Form Builder so it has the same theme and I can use any properties configured throughout the process.
Then add a "Terminate Window And Close Dialog" so that the project closes afterwards and EndDialog.aspx never shows.
Component Links
http://www.symantec.com/connect/articles/terminate-window-and-close-dialog
http://www.symantec.com/connect/content-external/workflow-id_LogicBase.Components.FormBuilder.Simple.TerminateWindowAndCloseDialog/workflow
https://support.symantec.com/en_US/article.HOWTO61749.html