In fairness im not sure Fern took that much moulding by Pep.
Prior to coming to City, when he was at Shaktar, he could do everything from playing as the deep lying play maker, box to box and or attacking midfielder, still can.
It was Pellegrini who deployed him as the deeper of the two between him and Yaya, which allowed Yaya to push forward for a few years.
Sadly my view is that it stifled Ferns game and although he has been brilliant, these last few years due to the demands placed upon him we've never really been able to see his natural game thgroughout a season.
Nevertheless in terms of the tools and abilities to carry out his current role Fern already had them, and more.
I think what was tweaked was Pep being clear that he wanted more from him than what Pellegrini has demanded which essentially was for him to sit deep.
Pep has asked him to be pivotal or more influential in Citys build up and attacking transitions from the deep lying deep lying midfielder role he currently occupies.