Qt デザイナー UI を再設計するときにカスタム コードの損失を防ぐにはどうすればよいですか?

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        [...]

    def retranslateUi(self, MainWindow):
        [...]

from Ui_MainWindow import Ui_MainWindow

class Logic(QMainWindow, Ui_MainWindow):
    def __init__(self, *args, **kwargs):
        QMainWindow.__init__(self, *args, **kwargs)
        self.setupUi(self)

class Logic(QMainWindow, Ui_MainWindow):
    def __init__(self, *args, **kwargs):
        QMainWindow.__init__(self, *args, **kwargs)
        self.setupUi(self)
    def closeEvent(self, event):
        answer = QtWidgets.QMessageBox.question(
            self,
            'Are you sure you want to quit ?',
            'Task is in progress !',
            QtWidgets.QMessageBox.Yes,
            QtWidgets.QMessageBox.No)
        if answer == QtWidgets.QMessageBox.Yes:
            event.accept()
        else:
            event.ignore()