I'm only new to this, but it seems you want to replace the original icons with your own.
If new ones are the same size, couldn't you just?:
- back-up the originals
- rename the new ones the same as the originals
- replace the originals
Then you wouldn't need any additional code for the extra icons, in fact, you wouldn't need to change any code. If you want to go back to the original icons you just overwrite the new with the back-ups.