IMO this POD could change Louis/Ludovik in my language/ behaviour. OTL, he had no male heir, so he maybe didn't care too much for Poland, because he thought that his line will not inherit Poland ( maybe he wasn't sure that Hedwiga could run the Kingdom ), so why bother much about Poland if they will become independent after his death anyway?
ITTL, with a male heir for BOTH kingdoms, he could pay much more attention to Poland than OTL...
The issue of names in this timeline is always going to be difficult.
I mean, I'm not actually using the Magyar name for Louis, which is Lajos.
I've been rather inconsistent with my choice of names. Louis is Lajos in Hungarian, Ludwik in Polish, and Ludovik in Croatian and Bosnian. Charles is Károly in Hungarian, Karol in Polish, and Karlo in Croatian and Bosnian.
So of course, I will probably opt for the English version of their name, Charles and Louis. Though, when dealing with the different areas of the empire, I just might opt for using their local name in the region.
I just haven't mentioned the Croatian version of their names because Croatia is an area I have less information than I would like on this period. I have some info on Bosnia due to a rather old History article, but not much on Croatia.
Also, I've been kinda inconsistent with which version of their names I go with
As for Louis' policy towards Poland, he might visit it more often to ensure his son's succession. But his policy will change towards it.
In OTL he tried pretty hard to make sure his daughters inherit. He gave the privileges of Kosice as I mentioned earlier which gave the Nobles a number of important rights in order to bribe them in accepting one of his daughters (in this TL, he is under no obligation to offer them the privileges, and he won't), and they did.
Just not the daughter he wanted.
In OTL, Louis wanted his daughter Mary to take both Poland and Hungary with her husband Sigismund. He even sent Mary and Sigismund to act as his regents in Poland right before his death, but unfortunately for Sigismund, Louis died soon after and Sigismund wasn't able to get a power base in Poland. The Poles subsequently kicked him and Mary out.
They then gave Elizabeth (Mary and Jadwiga's mother, not Louis' mother of the same name) an ultimatum: Hand over Jadwiga and we make her King, or none of your daughters inherit. She handed over Jadwiga, and the Poles subsequently kicked out her fiance Albert of Austria and looked for a husband of their own choosing instead. They chose Jogaila.
In this timeline, Louis might just spend more time in Poland, or his son might. Louis apparently died of something akin to Leprosy, so he might want to keep his son away from himself in his later years. Could send the boy over to be in Poland every once in a while to ensure he speaks Polish and that the Poles like the boy.