Nah, you can still get Septem's icon, no need for hard resets, it's just that the way to get his icon is by getting high affection with him.
Ik, ive already gotten it. you cant get the icon twice, and Nulla permanently removes the icon if you do his route AFTER septems. Nulla gets jealous that we have septem's icon and removes it in place of his. I have already gotten septems icon, it just permanently gets removed by Nulla if you do his route after such.