Like nick coloring, is it possible to modify the nick list to add information like country code?
If possible is the nick list would be available for normal functions such as voicing or opping?
Thank you all

The voicing/opping functions that you have mentioned are already available via the nicklist menu, under Control. As to adding information to the displayed nick in the nicklist, while it's theoretically possible, there would have to be something to distinguish the nick from the extra information. I don't use this program myself, but I understand that nicklust.dll has a lot of options not available directly through mIRC, so you might want to check that.