Rockstar North's co-studio head and head of development, Rob Nelson, has explained how and when players can switch between dual protagonists Jason and Lucia in GTA 6. He says there are some missions where you are forced to use a certain character, some where you are made to switch, and some where you can choose who to play as and change at will.
In an interview with Famitsu that's been translated by GamesRadar+, Nelson describes the team's design philosophy as it pertains to character switching and restriction. "Sometimes [switching characters] is limited by story progression," he explains.