I was kind of annoyed in Picard when the Changeling infiltrator was genetically modified by Starfleet. I thought it would have been way cooler if the physiological changes were a result of working alongside 8472, given that 8472 also wanted to infiltrate Starfleet and potentially didn't have the same blood test vulnerability.

I thought it would have been a neat reference but instead it's just another one of Starfleet's evil secrets.