Unless they changed it, there are several people who indicate that although you aren't changing YET, you will. It's only a matter of time, and when you change, it will be sudden and terrible, and everyone around you will die. Off the top of my head, these include:
The hag
The elf guy in the Hag's Lair who sees his reflection in the mirror
I'm pretty sure Gale says it or hints at it
I thought Halsin also suggested this
Nettie gives you a vial of Wyvern Poison BECAUSE she's afraid you'll turn at any moment
Raphael CERTAINLY says it
And I'm fairly certain Omeluum also says it. That's why he offers the ring, to help you prolong your situation to buy you more time
There's also the tiny little detail that, on the mindflayer ship, we pushed a button and turned a person
instantly into a mindflayer! I don't believe we have any reason to suspect our tadpole situation is different from that person. So it's perfectly likely that, at any moment, whoever has control over these tadpoles could instantly transform us. Maaaybe we would have to be captured and put in a special pod for that, but maybe not.
