It appears you want the user to push button 1 to select a file. You then change the label on button 1 to the path the user selected. You then expect the user to push button 2 to process the file selected when they pushed button 1.

Quoting out of order:
Quote Originally Posted by Sabre Runner View Post
What I'd like to do is to change the text of button 1 if and only if button 2's operation has reached the loaded successfully part.
Then why do you set it in the handler for the pushButton1 clicked signal? Line 5 in this chunk:
Qt Code: 
  1. void Window::on_pushButton1_clicked()
  2. {
  3.     path = QFileDialog::getOpenFileName(this, tr("Open File..."), path,tr("Files (*.*)"));
  4.     path = QDir::toNativeSeparators(path);
  5.     pushButton1.setText(path);
  6. }
To copy to clipboard, switch view to plain text mode 
This is the button that preps the path to be used to load the file from.
should probably be after line 16 of this chunk where the processing has been successful after the user presses button 2:
Qt Code: 
  1. void Window::on_pushButton2_clicked()
  2. {
  3.     try something...
  4.     catch one exception...
  5.     {
  6.         output error 1...
  7.     }
  8.     catch second exception...
  9.     {
  10.         output error 2...
  11.     }
  12.     catch all other exceptions...
  13.     {
  14.         output generic error...
  15.     }
  16.     QMessageBox::information(this,tr("Loaded"),tr("Loaded Successfully"));
  17.     perform some other operations and configurations for the future...
  18. }
To copy to clipboard, switch view to plain text mode 
You also need to ensure that button 2 cannot be pressed unless button 1 has been AND the user did not cancel the file selection. Something has to reset button 1's label too I guess.