So what do you do if you hit 5 letters across the two games? You wouldn't be allowed to add any new letters :)
For example Word 1 is PILOT Word2 is PLANK First guess is PATIO -
First Game returns P (in the right place) and T I O (in the wrong place)
Second Game returns P(in the right place) and A (in the wrong place) By the rule you have suggested. you must use all 5 letters in your guess so you cannot add any new letters :(
Guess I didn't explain clearly enough. In your example, for the second guess (and each time after that), you'd have to choose whether to use PTIO (without the A) or PA (without TIO). So, for each guess, you adhere to either all the clues you got on the left-hand word, or the right-hand word.
That's my way of playing hard mode for dordle, anyway. Perhaps you can give it a try 🙂