when u say 4 5 years.. i can tell you one thing.. there is nothing which can use to damage the wall...why ?

this is because after 1 or 2 years.. the wall original color will start to fade to another darker colour.. u can see this in typical old house.. however , if you cover the wall with a poster, after you remove the poster few years later, you can see the huge different.. the wall colour behind the poster are still in good condition... meanwhile the wall color which you everyday see actually faded away already

if your paint did not get direct sunlight everyday , then is okay to have second layer... if you have other colour such as light blue , light yellow.. second layer should be something darker to cover the first layer. when u have darker colour d.. you want back to light colour, unfortunatelly , you have to waste more money on getting the wall back to white color coz is always the first colour foundation if you want to have nice colour contrast in your house..