Transmission question

can I have the fill hole open with the truck running. For ex. I'd like to have my pump at the ready with the hose inserted about 1.5 inches in so if the trans needs like a quart more I can just fill till it drips out the overflow tube. I used to shut the truck off and them open fill hole and add a quart and then start truck again make sure I'm between 115 to 130 and open overfill tube to see if I'd added enough . I'd just like to be at the ready when at proper temp just fill while it's running until it drips out and be done. Tia