Will a vasectomy prevent genetic engineering of a child?
From the wording of your question the 'genetic engineering' that you are envisaging will involve sperm. So the question is really, does vasectomy affect sperm production?

The answer is that it does, but it doesn't abolish it. For example:


  McVicar et al. (2005) Effects of vasectomy on spermatogenesis and fertility outcome after testicular sperm extraction combined with ICSI. Human Reproduction 20: 2795-2800


These authors found that sperm yield fell to about 35% > 5 years post-vasectomy.