To avoid game crashing,i got a list what not to do with data.zip (if i miss something,you can post more)
1.delete the data.zip
2.modify the data.zip
3.delete graphics in data.zip (Will cause the graphic to very glitchy or lost all the tiles)
4.delete all the sounds in sounds folder in data.zip (Will make no sound effect,but game music still work)
5. do anything with data.zip
there is no reason to ever even click on the folder unless you feel like screwing up the game. any replacements for files in data.zip can be put in \Documents\VVVVVV\
this is the worst topic I have ever seen
if you ever want to access an unmodified copy of vvvvvv's resources you can copy it out of data.zip into your \Documents\VVVVVV
6. Do not speak ill of data.zip, or it shall become angry.
7. data.zip is your friend. Make sure to feed it twice a day.
Wanting to remove the built-in levels from the levels list is a perfectly valid reason to mess with that zip, it's what I did for V6HS (you know, that video which I was supposed to put on VHS and then back to a digital format and then to upload it)
The world isn't going to explode if you screw data.zip up, if you notice that VVVVVV crashes after doing something with the zip, then you know you did something* wrong and all you need to do is place back the original one to get it back working.
* that "something" can be using Windows explorer to modify the zip
8. data.zip is Terry in God form. Revere or you shall be punished by Veni Vidi Vinci