Extension Tubes, Close up lenses and and IS

If I use an extension tube on my OMD with a legacy 50mm lens do I need to set the IS for my lens at 50mm or do I need to make an adjustement because the the extension tube has changed the focal length of the lens. It seems like I read a long time ago that an extension tube changes the focal length and that there were tables of values somewhere that would give you the equivalent focal length depending on how many and what size extension tubes you used? Would I also have to do this if I used a close up lens in front of my Olympus kit lenses?

JPG