I drive a Toyota Corolla (E120, year 2000). It has automatic transmission with these options: P, R, N, D, 2, L. I almost always drive using "D". If I am driving at around 70 km/h (e.g. on level road or down a hill), is it safe to shift from "D" to "2" or "L"? Does the answer depend on whether or not I am pressing the gas pedal and/or accelerating while shifting?
While I am not familiar with this particular car, I would not think twice to gear down an automatic transmission if I'm going downhill and I need engine braking.
It is up to the transmission control mechanism to prevent the engine from going into unsafe rpm numbers. This means that you may or may not get the braking action expected, no matter how much important is this for you.
Anyway, the signs 1/2/3/L on the stick do not mean anymore "limit to the 1/2/3/lowest gear". What these mean on a model year 2000 or newer car is simply "I need my engine more responsive right now and I am ok with the increased fuel usage, wear and noise, so switch gears at higher rpm, please".
If you don't like this, drive manual. 20-ish percent better economy and a marginal possibility to break your engine by shifting gears.