Hasta La Motion!

Is there a way to access the render file type of a write node via expressions, TCL or python? Say, I have a switch to determine which part of the image should be rendered and I want to render one part as a jpg, the other as a png. Is there a way to set the render file type based on the switch position?

Another solution would be to have two renderers and swap names between them. So, my active renderer is called Write_By_List, the other is called Inactive_Now. When I alter the switch, the write nodes would swap names. Only the Write_By_List renderer is considered by my script…

Thanks for your help!
Jules