You may want to use the format of the source member as the definition of the target member, but replace some of the source values rather than reuse the segments from the source. For example, you may have a requirement to filter the source by the value of the 4th segment, then replace the 7th segment with an explicit value, and then retain the values of the other segments as in the following:
Source:
??????-??????-?-012000000-??????-???-???????-??????-??????-??????-???
Target:
??????-??????-?-012000000-??????-???-GROUP-??????-??????-??????-???