Is the technology advanced enough to manufacture and modify viruses to perform specific tasks?

Yes. We are already doing so, in fact. We use bacteriophages (viruses that attack bacteria) as a way to kill bacteria. However, there are concerns about dosage, potential horizontal gene transfer, and our own immune response that prevents them from being widespread yet.

 

http://www.nature.com/nrd/journal/v2/n6/abs/nrd1111.html

 

Actually, the above works with non-GM viruses as well.

They have tried to use retroviruses for gene therapy i think.

Is the technology advanced enough to manufacture and modify viruses to perform specific tasks?

 

Some viruses, yes. Baculovirus provides an expression system commonly used for protein production in insect cells by biotech companies. Bacteriophage (viruses that infect bacteria) are commonly used as cloning vectors.