Unless a halfie has a wild mom and is brought up and taught everything on how to be a wild rat, it would be a death sentence to release them. They would be killed by predators, real wild rats whose territory they are in, starve to death not knowing how to find food and water, and die from the elements.
It's always a domestic mom that escapes and gets bred by a wild male. She goes back home, or is re-captured, and 3 weeks later a whole pile of little agouti bubs are born. Surprise!
My first time I had NO clue they were halfies...I was helping out a woman in a different city online, with her domestic rat living in her backyard (someone dumped Rennie). Finally she caught her, I sent money to have her taken to the vets to have bot fly larvae removed, and a week later she gave birth to 8 little babies. Rennie was agouti hooded so agouti babies didn't surprise me.
But Bev never socialized them and when a rescue friend picked them up in Ottawa and took them home to foster until they could come to me...this is what she had.
They can jump like deer, startle easily, and that often means a bite if you aren't careful, can bite through leather gloves, are unhappy being caged but unless you socialize them heavilly and work around their issues they may never have a regular Out time like our domestics. They will break your heart as a lot of vets won't treat them, and they can have just as many issues as domestics.