If I used the option "copy disc" (not make disc) in nero for backup. Can it be written again or nero will automatically close it?
In case of you are burning "Copy disc" with Nero Express you can make additional copy if you want if you use Nero Burning ROM then you are copying from your hard drive which again you can make as many copy as you want.
Welcome to CDFreaks de2k6.
Yes, Nero will close the disc and you will not have the possibility to write more data onto it.