This mod works well to extend the boost indefinitely, but it's very difficult to disable boost. I've got to hit the left stick several times to get it to turn off. In addition, the screen effect is not always disabled. I'm running game version 1.0.1103.2, and I've got another mod that lets DLC cars persist; 'mpgunrunning in SP 7.0'
My configuration is as follows
"ToggleMode = false
DisableScreenEffect = true
DontKillShopScript = false"