I documented the procedure for creating inline reducing valves. This will allow you to have inline reducing gate, globe and ball valves (Others can added as well). When placed on a pipeline they will prompt the user for the new downstream size, set the valve size as Main Size X Reducing Size and adjust the pipe run to match.
The size will adjust when the runs are edited. The valves will also show in the Validation dialog if the Main Size and Reducing Size are the same.
I hope this helps,