Yes, I changed cards midway thru the exercises but that was because I had gone thru a significant change of focus in my life and I wanted a card that reflected the type of path I was on then.
You may certainly change your chosen card at any time. There are reasons why one card is a valuable consideration --- your view of that card changes over time, and these changes then can be easily applied to other cards and decks. Your choice, as always. Dave
If you have options, exercise them all.