In ASP.NET how can I add HTML to an aspx that I can't modify
<p>I have a .aspx file and would like to add some HTML to it. The problem is that it can't be modified. If I upgrade the product, this .aspx file will be overwritten and my modifications would have to be done again. </p>

<p>This is an open source product, so I can have a look at the codebehind. Again, I cannot modify it because that would break my upgrade path. Also, I need to add functionality that would never be included in the product, so sending in a patch is useless.</p>

<p>The class that's referred to is a partial class, so I tried implementing an extra Page_PreRender by creating another partial class of the same name in the same namespace. However, since this is in another assembly, .net says it doesn't know which is the correct class. </p>

<p>Is there any way I can do this?</p>
