Once you have finished the campaign you can reallocate perk points when replaying a mission.

[As Mapache points out in the comments, this only works if you replay the mission by clicking 'Play' then 'Continue' from the main menu, clicking the 'Missions' tab at the top of the screen, then choosing a mission from there. If from the main menu you click 'Play' then 'Mission Select' it functions more like starting a new save file from that mission.]

If you are asked to choose your characters, you will also be able to reallocate their perk points.


Once you have started a mission, but before you breach the door, long click on a character portrait to show their perks.


Once you can see the character's perks, click on the perks you don't want to use in order to free up points. Then select the perks you want to try.


Characters have a maximum of six or seven points available. You cannot unassign their anxiety dream perk.


Repeat for all characters in the level.

Once you're happy with your new loadout click done at the bottom right, breach and enjoy!

When you complete the level your perks will revert to the loadout you had at the end of the campaign.