Well sure, if you're talking about the sympathetic system, but for the parasympathetic system, L5 is about as close as you're going to get for the lower colon, as the sacral nerves S2-S4 are involved in the portion of the descending colon, past the splenic flexure. Above the splenic flexure, you need to go up to a C1-C2 level, to try and affect the Vegas nerve. Also, as a Gonstead enthusiast, it is good practice to identify the lowest subluxation and establish a correction to relieve pressure, caused by lower spinal misalignment.
Pete