Sylas is a good example cause you have to now balance sylas r with ever new ultimate that comes out. Also like sivir shield. Do you need to put files in the game so that the sivir shield can block all new abilities? Sorry was just wondering. Have a good day!
They should, but they don't. This is what creates what some call "power creep". Certain champions become less potent based on new champions that come out. It'd be extremely hard to rebalance everything with every new champion, which is why competitive games should really be derived from the players and their choices, rather than a set roster of existing builds.
I skimmed through and misread your question. The "balance" part threw me.
No, they don't. Games run on what's called an "engine", which basically is a system of programming shortcuts that allow them to design the game more efficiently. Game engines allow developers to, for example, tag specific code ingame as an ability, a basic attack, a shield, etc. Thus, when they make a new champion, they would simply say that all of their abilities classify as abilities, and because Sivir's shield blocks abilities, it'll automatically register that "Hey, this gets blocked!"
Likewise, if a new item with an on-hit effect is implemented, because Yasuo's Q is designated as a basic attack, the on-hit effect automatically applies with no extra coding.
It's probably not exactly like that, as it varies by engine, but that's the principle.
Title: True Story
No i dont think they do because its a coding thing where an ability is registered as a specific category..you referenced Sivirs E as a good ability...There is a script that goes into the interaction so when a skill matching the code comes in contact with the other skill they have a programed action in place..
Does that answer your question?
No, Sivir spell shield blocks anything considered "CC" or an 'ability'. The ability in question may have coding to ignore an interaction but that doesnt involve changing the script of older items/abilities.
For instance, if a champ has a self-cleanse ability they dont put the interaction in Mordes R; just "if suppressed, cleanse." And since Morde r is a 0.25 suppress its cleansed
yes they HAVE to but they dont. if they would, there wouldnt be THAT FUCKING MANY bugs.
When they developed Sylas they had to re-script every single champion's ultimate.
Specific ultimates have specific interactions with his abilities.
R and 
R are 2 ultimates I can think of who have specific interactions when stolen by Sylas.
