No you can not just dig it up and replace the pipe. The reason is the ground is what absorbs the waste water. When a drainfield goes sour its because the ground has become completely saturated and simply will not take any more water. Also as a DYI most all counties want someone who is licensed in this area to preform the work as there are a lot of things to take into consideration. lay of the land, trees, city or well water, property lines and more.