I would think that since Omega owns every other computer he looks at, per Chris in Rogues, it seems reasonable that he could indeed reprogram Caeco’s nannites.
As far as Tanya’s personality goes, her personality has changed over the course of the books, but most of it I would consider normal considering everything that happened to her and Chris. That being said, the constant sniping at Declan and Omega is getting tiresome, especially since she was the one pushing so hard for his creation. This is s prime example of being careful what you wish for. Hopefully the next book will shed some more light this subject.
The problem, if you can call it that, with having so many engaging and interesting secondary characters is that people want to read their tories too! What is an author to do! LOL!!