Merge ResX file at runtime?

I'm generating/constructing from code a custom .Net managed resource file (a .resx file)

In C# or VB.Net, how I could design a method capable to merge, join or embbed my custom .resx file into a .net assembly (more or less in the same way that VS compiler does by default)?

So, in one hand I have a Application.exe (already compiled), and in the other hand I have a resources.resx, my intention is to "merge" the resx into the compiled assembly.

Any sort of info will be gratefull, because I didn't found nothing about it.

PS: The only requisite is not use 3rd party tools such as ILMerge.