Modify the final ISO image new
There are times when you need to modify certain files in the final CD. Why you ask? Because you don't know how to code or compile and have a binary file ready, or the file doesn't come from our tree, or just for testing purposes. In case you want to know how to add files see slipstreaming.
To do it you could use an iso utility, such as UltraISO.
First, build the iso image:
This will create the iso image in this location: \output-mingw-i386\reactos
(location depends on your platform (i386 in this case) and on where you downloaded the source code in your computer).
Next, install UltraISO.
Third, navigate to the folder that contains the ISO image and right click on the ISO file and select "Open with UltraISO".
Click "Continue to Try..."
Modify the ISO image as pleased
Save the modified ISO image: