If code/script needs fire every time a variable gets a new value that variable should be private, and you should write functions in the blueprint to “get” and “set” the value of the variable.
In the “set” function, you write the logic to compare the new value with the old value and determine if the variable increased or decreased (<, >, etc.).
If you need multiple different blueprints to run code when the variable is changed you can use an event dispatcher.