Yes, it's true, there were some changes made in the second half, to secure the condition of his best players. But it's true that it wasn't a big change, because Hansi Flick didn't want to take more risks. He was actually quite confident with his team's performance that they would definitely win, especially since they were ahead in the first half. But after that, he regretted it a bit because he felt he made a few mistakes in the second half until Espanyol's goal happened in the 65th minute.
Source: Barcelona stats
With this match, Hansi Flcik was really able to bring Barcelona to its top performance by optimizing his players, especially their front players who could do it optimally. Lewandowski with 14 goals, Rapihna with 7 goals, and Yamal and Olmo with 5 goals.
Lewandowski is a main goal source for Barcelona but they have many attacking players and it's impressive that they have many players already scored goals for them. The list of scorers for Barcelona is long and shows that they have different attacking solutions for finding goals with many aces under sleeves. Lewandowski is playing well but he is old and his performance quality will probably drop in second half of season.Source: Barcelona stats
With this match, Hansi Flcik was really able to bring Barcelona to its top performance by optimizing his players, especially their front players who could do it optimally. Lewandowski with 14 goals, Rapihna with 7 goals, and Yamal and Olmo with 5 goals.
Hence, Barcelona need other players to cover this issue for Lewandowski and they will win La Liga trophy if they succeed to do this task. So far they have been doing this task very well and their young players will show their bigger contributions in this season, when they become more experience by playing more matches.