What I want to do is to programmatically update resources of an executable file.
I have a binary resource (.res) file containg bitmaps, icons, version info and a manifest, created with a resource editor, and a PE file compiled with AutoHotkey to which I want to copy the resources from the .res file.
Until now I used to do this with ResourceHacker in command prompt, but ResourceHacker can't be redistributed and besides I want to do this more elegantly.
So I was looking in the WinAPI functions and there seems to be a way to do this: http://msdn.microsoft.com/en-us/library/windows/desktop/ms648008%28v=vs.85%29.aspx
But the problem is that the article describes how to copy resources from an executable file to another, and you can't import non-executable files (the .res file) with LoadLibrary/LoadLibraryEx.
There also seems to be a way to do this with tools from Visual Studio, particularly LINK.exe. But I'm not sure if it can be used outside of the VS enviroment. I have no idea how it works.
You can programmatically update resources with the UpdateResource function
RES files are not involved. RES files are used by the project makefile system to enable minimal rebuild of resources... they don't have to be recompiled every time the application is relinked, just embedded. But you aren't relinking the application and losing the existing resources, so updating just the resources you want to change is the way to go.
If your source assets are already encoded in RES files, then this page describing "Resource File Formats" can help you extract them. It also describes use of LINK.exe for resource embedding. LINK.exe is installed as part of Visual Studio, but it is also available in many versions of the Platform SDK and Windows DDK.