It depends ...
if the country to be added to the list is backed by, say, the US, then maybe no serious global effect is expectable offically, at least among the Westerners which control the main global media and misuse their power to control world-wide institutes as far as they could, and hence the effects are limited probably to regular people who mainly can vote for other officials in future, and limited to politically independent countries which can use the situations to manifest the Westerners' hypocrisy/double standards.
But if the country to be listed is not backed by the US and its Westerners allies, probably withstanding them, things can differ magnificently, as they often use any possible excuse to bit their enemies, organizing the whole community around a good concept against their enemies, like they usually misuse human-right concept. Sometimes a single woman dies in a doubtful manner and virtually every known and unknown Westerner politician react and a flow of anger/hate is conducted to smear the face of their enemies globally, and this affect that enemy in several aspects; on the other hand, sometimes thousands of kids/women are killed with no doubt about them being killed out of oppression and virtually no one care and even any flow of objection is condemned again virtually by all such politicians.
Therefore, it can have effect and indeed has effect, but the quality/quantity varies over likes/dislikes, and capabilities individuals/officials have to affect as much as they could. Consider it as a News/excuse that is declared/confirmed by a usually assumed accurate source. Those who like the News will try to promote it and use it for their interests, and those who dislike it try to withstand it, either ignore it and request for everyone to ignore it, or to misinterpret it, or suspect in the authenticity of the source. How different sides benefit/withstand a News is itself a kind of war ...
Update. In case a reader will assume this answer not addressing the specific question asked, the question has three parts:
- "Why does the U.N. maintain the ... list"(?)
- and "how does it affect entities that are added to it"(?)
- and "particularly how does it affect Israel which was recently added?",
and a general answer is tried to be given here, no claim for it to be comprehensive at all, which anyway can also be restricted on Israel particularly as it is heavily supported by the US and other Westerners. The News that says Hamas is also added to the same list, although the questioner is not interested in, again follows the same rule. But why Israel is bolded here, might be due to previous propaganda by Westerners, that Israel is so good and Hamas is so bad, so that the recent News now seems to be an inflection point about Israel but not Hamas in the eyes of many audiences. Hamas has always been condemned, but Israel was always glorified even more than God is glorified, so much that people can object against God easier than objecting against a group of people who was once chosen by God! Therefore, so strongly that Israel is supported by the US and other Westerners, "then maybe no serious global effect is expectable offically, at least among the Westerners which control the main global media and misuse their power to control world-wide institutes as far as they could, and hence the effects are limited probably to regular people who mainly can vote for other officials in future, and limited to politically independent countries which can use the situations to manifest the Westerners' hypocrisy/double standards"
