The section you reference, "Swapping Spells in Your Repertoire" from PF2CR#193 does not specify how you cannot swap out bloodline spells, only that you cannot do it. Immediately after, it also defines another instance where you might be able to swap the spell...
You can also swap out spells by retraining during downtime.
To me, this means that the statement, "This spell can be a cantrip, but you can’t swap out bloodline spells," applies to the section "Swapping Spells in Your Repertoire," as a general rule for swapping out spells. Additionally, my quote above references the Retraining heading on PF2CR#481, which states, "Your GM determines whether you can get proper training or whether something can be retrained at all," meaning that your GM has the final call. It also states "...a sorcerer can retrain their bloodline only in extraordinary circumstances." Given all of that, were I the GM, under less-than-extraordinary circumstances, I would say, "no, you can't retrain it," and the very max I would allow (even under extraordinary circumstances) without a full bloodline change would require it to be of the same spell list/tradition.
Logically, I also feel like the nature of the Sorcerer (and bloodlines) is that they are part of your very essence, flowing through you.
For me, the combination of role-playing-nope and logic-nope make a pretty hard "nope." Hope this helps.