It's a sensible question and you are right to think about possible difficulties, sometimes you can have problems if one cat has just been at the vets overnight. They recognise each other so much by smell, and one that has a new smell could need time to settle back in with the group. Sometimes you can rub some baby powder into all their coats so they all smell the same, or you can take some bedding and swap it over so they get each other's smell on them.
If you are aware of the possibility, and are careful with reintroduction, then hopefully there won't be a problem
Cats can vary so much in their reactions, and a lot depends on their individual personality and also on the closeness of the bond they have with each other.
There are products you can buy to help ease moments of tension like reintroductions. Some people find feliway diffusers or sprays helpful

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