Football changed in 2008: Pep Guardiola became the manager of Barcelona. Football had been evolving anyway. There had been amendments to the laws to encourage more technical, attacking football (the backpass law, the liberalisation of offside, the crackdown on intimidatory tackling). There had been changes to the economics such that the gulf between rich and poor had grown. But what Guardiola achieved at Barcelona with a supreme generation of players shifted the parameters of what was believed to be possible. It is that philosophy that continues to guide him and has underlain Manchester City’s success over the past two seasons. On the very odd occasions when things go against his side, Guardiola can be prickly about that. “I won 21 titles in seven years: three titles per year playing in this way,” he said in his trophyless first season in England. “I’m sorry, guys. I’m not going to change.” It is true in the broadest sense but manifestly false on a more macro level. Guardiola is renowned for the research he does into opponents: he is forever striding through Martí Perarnau’s books, clutching portfolios of information about his opponents – what would be the point of that if he didn’t…