Actually you don't have to overwrite. The name has to be the same. If you want to still keep the original files, rename them and add something like -Old to the file name. i.e. DVD-Old.png. Then save the new file as DVD.Png and it will use the new DVD.png file.

I thought I could use this Tutorial to customize and use my own icons for a blue ray player. The player also has the colored buttons on the remote: Red, Green, Blue & Yello so it wold be nice to have those as icons on the remote. I did as per your example and made an activity called "favorites". After I was all done with the browser step, I went back to activities and clicked on the activity "Watch Blueray" that was originally created and checked it and clicked delete. However, it looks like it was done, but the system will not let you actually delete an activity based on a device. That sucks. So basically i guess there is no way to do what I want without having two activities for the same device - My custom one and the original one.