modify(e, 'xp_score')

Syntax

modify(entity, 'xp_score', value)

Manipulates player xp values - 'add_xp' the method you probably want to use to manipulate how much ‘xp’ an action should give. 'xp_score' only affects the number you see when you die, and 'xp_progress' controls the xp progressbar above the hotbar, should take values from 0 to 1, but you can set it to any value, maybe you will get a double, who knows.