if you have a rooted device you can use titanium backup to restore data as long as the account used was not connected to Facebook or google play.
but the data does still sync to the server!
there are no current mods for racing rivals for money or gems past 4.3.1.
to easily get money i suggest getting 2 devices, one with your main account and one with nothing on it, dont connect the second device to google play or Facebook, and race until you get to the viper, mclaren section of the campaign, only takes a few hours, then transfer all money and cars to your main account.