Dear Pierre:
I am a newbie, so I hope for your sake that someone more experienced responds to your question. However, I thought you might be interested to know that I have been having the same problem for months now with understanding how the dipole moment is calculated in CP2K. I don't think there is anyone around who knows about this anymore because I asked several questions myself some months ago and have not had any luck with responses. I suspect that whoever implemented dipole moment calculation in CP2K may have left the group. Unfortunately, I don't know of any other resources that might help us.
I'm running ab initio simulations and do not want to use Berry Phase. I didn't realize I was using it until I had already run some resource-intensive simulations and now I can't find out how to do a conversion. I'd even run the simulations again, but it seems there's no alternative to using it in CP2K. So I think the answer to your first question is yes. I can't answer your second question. Good luck.