The rules for hiding (PHB 177) has an interesting clause, which makes it distinct from many other contests.
When you try to hide, make a Dexterity (Stealth) check. Until you are discovered or you stop hiding, that check’s total is contested by the Wisdom (Perception) check of any creature that actively searches for signs of your presence.
Here we have a contest where you make a roll at one point in time, then at later points in time that roll’s result is contested by another party’s roll.
Is it possible for someone who is already hiding to increase their Dexterity (Stealth) check total without re-rolling their check? Possibly by application of guidance, pass without trace, Epic Boon of Fate, or a similar ability? Or is the check total immutable once the initial check has been made?