Such mass interventions (typically by Western countries) have become fashionable since the The Gambia v. Myanmar and Ukraine v. Russia, particularly in genocide cases, which involve multilateral treaties that provide the procedural route for the interventions. Both cases are still ongoing, so hard use as a basis for an answer (as to impact of interventions at the ICJ). BTW, such genocide cases can take an extraordinary amount of time to adjudicate at the ICJ: Croatia v. Serbia took 16 years: 1999-2015, even though there were no interventions in that one!
Whether, more historically speaking, such interventions make any difference to the outcome is hard to say, but it seems rather they don't:
E.g. in first such case that usually discussed, which was before ICJ's predecessor (the PCIJ):
it does not seem Poland made any substantive arguments of its own, after being admitted to intervene. In the oral proceedings, the Polish Agent ‘stated that he agreed with the arguments and conclusions of his colleagues, and would not make a special statement on behalf of the Polish Government’.
In the next case (Haya de la Torre):
In practice, Cuba’s intervention came down to a brief speech at the end of the oral proceedings.
A somewhat more complex intervention was New Zealand's against Japan in the Whaling case, initiated by Australia. But it's hard to say what difference it made (other than setting some bad procedural history) since the two countries "colluded" rather openly, and so their statements were very similar.
Shortly after Australia instituted proceedings in the Whaling case, the respective foreign ministers of Australia and New Zealand ‘agreed to work together towards the elimination of whaling in the Southern Ocean through complementary strategies’. Otherwise, in a joint statement of the two states, it was noted that:
Australia has indicated that they would prefer New Zealand not to file as a party. Because New Zealand has a judge on the ICJ, Sir Kenneth Keith, the joining of the two actions would result in Australia losing its entitlement to appoint a judge for the case. New Zealand’s decision to intervene will allow the case to proceed without delay.
[...] during the second round of oral proceedings, Japan criticized New Zealand for entering into issues beyond treaty interpretation in its observations. Referring to the abovementioned joint statement, Japan stated that ‘the two parties have acted in collusion. It is difficult not to conclude that they are parties in the same interest. This is an unfortunate precedent for Article 63 interventions. It has clearly prejudiced Japan in these proceedings.’ However, neither the Court, nor individual judges, appear to have addressed Japan’s grievances.
So, New Zealand was able to "game the system" there a bit, but it's not clear if that made any difference in the outcome of the case, which was 12-4.
Furthermore, Greece intervened in the Jurisdictional Immunities of the State case, but they still lost alongside Italy, who had initiated the case (12-3 to 14-1 depending on the issue.)
So, IMHO, the YNet piece is rather overselling what interventions at the ICJ have legally achieved, thus far. I've looked at a couple of additional (shorter) pieces on this 1, 2, but none mention some case turnabout resulting from interventions at the ICJ.
It's also worth noting here that at the ICJ a judge is not required to recuse themselves on a case involving their own country. (That's because, technically speaking, they are not representing their country.) Even the formal rules for recusal that are much narrower, involving a judge's prior involvement with a case were rather ignored in the court's early history, but less so recently; see Giorgeti, pp. 8-9 for details on that. In fact, the ICJ rules allow parties to the case to appoint an ad-hoc judge on their behalf for a case, and typically a country will appoint a national in that role, but they don't have to.
(The quotes in this answer are from the first piece I linked: Keeping score: an empirical analysis of the interventions in Ukraine v Russia
by Kyra Wigard, Ori Pomson, Juliette McIntyre, not from the Wikipedia or ICJ summaries. I've linked those for more context at the OP's request, below. Some ICJ cases seem obscure enough to not even have Wikipedia pages; those I've linked to their ICJ summaries.)
