Yes for a short period of time. Viral infection can cause unbearable symptoms and may even lead to death if your immune system is compromised. Few weeks ago, when I was infected with the stomach flu viruses, I had absolutely nothing to do other than waiting patiently for my immune system to be activated. Is there other ways to treat viral infection, other than the well-known antiviral remedy, such as vaccines, Tamiflu and HAART?
A pediatrician pointed out the possibility of deriving viruses to target virus-infected cells last week at a Christmas party. To design such virus, one must recognize the receptors required to enter the cells. To target virus-infected cells, these receptors must be the same for the designed virus to enter. The designed virus can potentially do several things: hijack the replication machinery to repress harmful virus to replicate; repress the transcription of specific cellular factors that are required for the replication of the harmful virus; induce apoptosis (programmed cell death) quickly.
The first point that I proposed may not be the best due to the fact that harmful viruses can still be replicated but at a slower rate. In contrast, the second point that I proposed can potentially inhibit harmful replication at the maximum level but may be detrimental to uninfected cells if the cellular factors are essential. The last point may not work due to the same reason as the previous point.
Another restriction on the design is the rapid mutation of the viruses. RNA viruses depend on the error-prone RNA polymerase to reproduce its RNA genome. For instance, HIV virus is estimated to have mutation in every single basepairs in its genome in just 24 hours. Thus, restricting the expression of cellular factors may repress viral replication for only a short period of time.