[Slice]

The include line is wrong, it should be <a_samp>. It would keep switching. bool:! is redundant (just use !). Using both IsPlayerInAnyVehicle and GetPlayerVehicleID is redundant (you can just get the ID and check whether it's 0).

Also, IIRC OnPlayerUpdate is called prior to OnPlayerKeyStateChange, which means you should just use GetPlayerKeys inside OnPlayerUpdate and return false if fire is being helt. That, however, would result in players being able to hold fire to desync themselves. If you make it disable only when pressing fire, players can just hold fire to get rockets synced.

I'd say it's safe to say that code won't work.