Hi Marie,
So what's the questions?
As the documentation and kris mention the process don't care about the version. If you change your process and keep the same id you can end up with strage behavior during runtime. It will depend on the process complexity and the changes that you apply. The engine knows the processes by the ID and if you change the process and keep the ID the engine will treat it as the old one.
The problems will start to appear when you have multiple processes instances in different stages and you change your process definition using the same ID.
My Two cents ..
Greetings.