How to call library functon on field change?

Summary:

Hi, is it possible to call a library function when a field is changed?

Content (please ensure you mask any confidential information):

In Transaction Line, we have a custom field to show the sum of its children rows. It's used to show total price of a model, summing the prices of the model children parts.

We have a library function that does the logic, and this function is called on "Advanced Default - After Formulas" for Transaction Line, and is also called in Save action.

We wanted to call the function whenever the user changes the price for a part in the transaction line, so this field would show the updated value before the user hits Save.