Regarding Bashir-Changeling not harming the baby one found in "THE BEGOTTEN", I had a theory on it since it was first revealed he was a Changeling, back in its original airing.
The Female Changeling in early season 6, I think it was in "BEHIND THE LINES", tokd Odo that they forgave him for killing that Changeling years ago. I think it was no accident they happen to find a baby Changeling, and I think that Bashir-Changeling was the one that set everything in motion, and ultimately 'told' the baby, by linking with it, to merge with Odo and make him a Changeling again.
Which also led me to another theory... I think Bashir-Changeling WAS the Female Changeling posing as Bashir. We see that runabout destroyed, but the Dominion can transport light years away... Eris did it, that Vedek did in "COVENANT". That Changeling would certainly have done that before getting killed.
Which also led me to another theory... the Female Changeling is Odo's 'mother', for lack of a better term, since we never fully understand how Changelings are born. Notice every other Changeling has had an issue with him after he killed Krajensky-Changeling... except her. She even said bringing him back was more important than the Alpha Quadrant. For my money, it stands to reason she would be the one to put into motion all the things that would give Odo his abilities back. She knew he had to be punished, but she didn't want it to be permanent.