Yugoslavia did not complain about having to switch to a different name - they just continued using it. From Wikipedia:
".yu was the Internet country code top-level domain (ccTLD) that was assigned to SFR Yugoslavia in 1989 and was mainly used by Serbia and Montenegro and its two successor states. After Montenegro and Serbia acquired separate .me and .rs domains in 2007, a transition period started, and the .yu domain finally expired in 2010.[1]"
You can make a case it's somehow really culturally important, but nobody will buy that as it was mostly irrelevant then, thus it's only relevant if you have an axe to grind.
From my point of view, people in Ljubljana had every right to continue using the .yu domain if they wanted to, and they could've maybe made a deal to manage the domain together. But it seems to me this collides with the desire to be independent, so my assumption is they were kind of happy to switch to their own tld. Or maybe you know this is not the case?
According to the article they kept running the domain and using it for email for two years until Postel transferred it to Belgrade. (The article phrases it as though that email use was less important or less serious than the unspecified "work" that the group in Belgrade wanted to use it for, but that smells like a slanted narrative to me)
http://www.london.mfa.gov.rs/ambassador.php
So it is rationale/fair for the states to inherit what they originally had paid for.
Speaking of inheritance, did the newly created states of Croatia and Slovenia in 1918 inherit their share of Austro-Hungarian debt when they left that union, or did they enter a union with Serbia debt free?
Much like in a divorce, if it's something that has clearly stayed separate the whole time then perhaps, but if it's something the combined state has shared and maintained then probably not.
Given that it was embroiled in a dispute over the succession of Yugoslavia for the entire time that it was calling itself "FR Yugoslavia", and that dispute was resolved shortly after the country changed its name, no, it's not at all obvious that it was accepted.
> The question of it being a succession state is not really relevant for the name.
The question of it being a successor state is what's relevant for the domain name though. Just because you have the same name as a previous state doesn't mean you're entitled to that previous state's domain name, just like with the UN seat.
> it's a big stretch this was the case for Yugoslavia in 1992 when the internet barely existed and the .yu domain existed for three years (according to the article).
Who inherits the petty cash tin in the embassy in London is obviously a much smaller question than who inherits the building. But it still all has to be negotiated.
> So in reality it's a nothing burger, unless you have an axe to grind.
That goes both ways though - if "FR Yugoslavia"'s position is that it's a nothingburger then they can't complain about having to switch to a different domain name - and if they wanted to keep using the domain name they had been and it would be a pain to migrate, well, so did the people in Ljubljana. Ideally they would've come to a negotiated agreement to either continue to share the domain, or make a smooth transition - but like with anything else, if you can't reach an agreement on how to split it then you don't get to just take it.