Is it possible to put a flag so the game starts in window mode?

I can't play in fullscreen (blackscreen) but it works in window mode but I need it forced so it starts that way, because if I use an application to do this I activate the bordeless thing after it starts and the game starts to react funny (mouse cursor position is not exact, sound disappearing, fonts aren't correctly written).

I've had this issue before with other games and I solved it by forcing bordeless window from the start rather than using a trigger after the game has already been started.