Is there a plugin / simple way to change terrain’s shape due to tire’s movement? For example, if you drive a jeep on sand, low speed and one wheel stuck on a big rock, you will be digging through the sand.
Is there a way to achieve this in unity3D?
There’s no simple way to do it, no.
You need to either deform the terrain under the tire or use a mesh for all/part of the terrain and deform that. The latter is possible (I’m not 100% sure about the former) but it’s not a trivial thing to do.
Alternately, if you just want to show tire tracks, that’s a bit easier to do. Search around for information on decals to get started.