No, it should not affect your achievements .
Unfortunately, though perhaps unsurprisingly, the answer is yes, the use of cheats will disable achievements and trophies .
Rockstar won't let you have mods when playing GTA Online, otherwise, you would get banned . Mods are only allowed for a single-player mode. …
As a result, your account will get restricted from using online mode. If you are going to use mods, use them in offline mode to prevent your account from getting temporarily banned from online mode .
In a new Q&A on the Rockstar Newswire, the GTA 5 developer confirms that players won't be banned for using single-player mods . … It also bears mentioning that because game mods are by definition unauthorized, they may be broken by technical updates, cause instability, or affect your game in other unforeseen ways. »
So no, it's not just about single player/multiplayer always, not exactly. For example, if someone installed cheats to "mess around" in single player, then they forget and connect to a VAC secure server in the future, and VAC detects the cheats, the account gets VAC banned.
No. Once a game has a mod enabled, you will not be able to unlock achievements or trophies . If you wish to unlock achievements and trophies in your game, you will need to disable all mods and revert to a save game prior to the mods being enabled.
Achievements / trophies will be disabled by cheats , and they will not be reactivated by them.