so 2 things..
1: you are correct it doesn't tell you other than about achievements not be achievable until later when you try to modify it via loading the save game and editing the game settings; I agree this should be able to be turned off at a later point.
2: there is a way to do this in the interim where if you launch with -devMode (this can be done via properties of an app shortcut or by adding it in steam and has been covered by many players)
2A: When in devmode you can keep giving yourself money until your at a point your comfortable with AND it bypasses the achievement blocker. For instance if you want to unlock everything, do it with the devmode menu in the same place as giving you 500K at a time.