I’m guessing that his source is likely Father Amorth himself, who is the Senior Exorcist of the Vatican. He was not very pleased with the redrafted Rituale Romanum of 1999 and 2000, which had not been altered since 1614.
It was not that he did not want any changes, he gave some indications that he did wish to see more appeals to the Blessed Virgin in the ritual. His problem was that the group of Bishops that oversaw the changes did not include any expert opinions from him or his exorcist colleagues, which up until that time had been the protocol of Vatican II (that is to include experts and generally follow their advice). That is why he has made statements against the new ritual. Also, he tends to be a man of outspoken opinions - but also a very highly respected exorcist (and authority on Our Lady).
Luckily, there was a clause inserted that exorcists could still use the old text if the local bishop approves.
I do not believe that this has anything to do with satan influencing the Vatican. I think (and Father Amorth hints at this as well) that the real issue here is that exorcism is a touchy issue for the Church. In highly modernised western democracies it is considered “out of date” and a relic of medieval times. I think the revised Rituale Romanum is an example of the Church possibly trying to hide something that she believes, but does not want advertised too publically.
But is that fair to the exorcists of the Church? Clearly not, hence the outspoken statements of Father Amorth. Exorcists in general have little support and many Bishops simply quit appointing them.
I suggest doing a search for Father Gabriele Amorth and some reading on exorcisms, but make sure the sources are worthwhile. Perhaps a poster or moderator could give us some good sources to read on this topic?