What was the first video game accessibility mod, at least for public gaming? Quite probably a simple booster crate, stool or chair to help small people reach the controls and see the screen.
Personally, one of my earliest arcade memories is of my Dad lifting me up so I could hold the flight controller and see the bombing run in Atari's 1978 game Sky Raider. Not the most comfortable playing position but better than not being able to play.
The first time I recall feeling disabled by a game, was on a Cub-Scout trip to see Superman at the cinema. There was a huge commotion around a brand new Space Invaders machine towering above us all in the carpeted foyer. When I eventually got close enough, I realised that I was too short to see the bottom of the screen, where your cannon is. Happily it wasn't uncommon to find a booster crate or chair propped up against the odd machine (especially so in pub arcades) so more little people like me could keep feeding the machines 10p coins.