It is possible to edit and bulk update Item Number values to suit requirements.
Changing the serial number
To change the numeric value of an Item Number, select Change Serial from the dRofus Ribbon Menu and you are provided with a panel which allows you to replace the current numeric value with a new value (but only if the resulting Item Number value is unique for that Item Group).
Consolidating Item Numbers
For example, if several Items have been deleted from the Project leaving gaps in the Item numbering sequences and the user would like to consolidate and order the numbering on the Items remaining then the following procedure will allow you to do this.
The option to Renumber is available when you right click on the lowest level of the relevant Item Group in the Item Group hierarchy:
The Item Numbers are regenerated to be sequential and without gaps: