Retroviruses, such as HIV, have a genome that is composed of RNA. Once inside the host cell, that RNA is reverse-transcribed into DNA; it is that DNA which is inserted into the host genome. All retroviral genomes are integrated through insertion; there is never any replacement.
Some retroviruses do, however, disrupt normal gene function. Mouse mammary tumor virus (MMTV) or Human T-lymphotropic viurs (HTLV) will often insert inside or near host genes termed "oncogenes," that, when disrupted, can lead to cancer formation.1,2 Viruses could cause up to 15% of cancers in humans.3 So, no actual genetic replacement, but there can definitely be genetic disruption and a deleterious functional change.
This ability, to insert new genes, has recently been touted as a new way to cure many diseases. Here's the most recent case, where the researchers used a retroviral backbone to insert a functional gene into some children; i.e., genetic engineering (Side note: Every time you see an article saying how scientists used HIV to cure a disease or something, this is what they mean. It's akin to calling dental X-rays "giant death lasers that fight cavities."). With luck we will get better and better at it, but right now it's only successful in limited cases for very specific diseases; massive genetic engineering of humans is still far off (unless you count bone marrow transplants).