Hello, Lepthturn is right, you're Hobby Shop is wrong. You can do many upgrades to your Amp, big or small and it wont break, unless you purposely run it into a curb at full throttle. Yea you probably will break something. There's little things you can do to upgrade and bigger upgrades you can do.
Below is one of my Amps totally upgraded to the max and I'm still looking to do some more upgrades to it. I do not baby this Mt., when out running, day or night, its at full bore. Wheelies, flips and tumbles, its like a Timex watch, it keeps on running. This Mt. has a high velocity fan mounted on the servo cover that keeps everything on the chassis cool and a high velocity fan on the motor to keep the heat down. You might call it over kill, I call it, heat prevention. As you do these type of upgrades, adding aluminum parts, bigger batteries and auxiliary batteries you add weight to the vehicle which will cause the motor having to work harder, which creates heat, hence the fans. At some point you might have to upgrade to a higher KV motor.
Point being, start small, bigger tires, 2S LiPo, maybe some turn buckles and see how things go. The Arrma Senton is a great 4x4, I have one myself and so far the only upgrade I've done to it is, bigger tires, Led lights and high velocity fans.