It is possible to get promoted to a higher league even without planning to do so.
In such cases, the players' salaries are usually lower than the minimum total salary required for the higher league.
If you choose to recruit new players, the suitable tactics might be completely different from those used before.
In this situation, the team is already relatively weak and is further punished by changing tactics, which feels like a double damage.
True, I hadn't thought about this. Thanks for discovering it.
It could be solved at least in part by doubling the effectiveness of preseason training or otherwise lowering the training level of all teams during the "Interseason Break."
Thus, the teams that have to change tactics due to the new squads will be only slightly at a disadvantage in the first days, but after two or three weeks they will have to achieve the maximum possible performance again.