Unit of measure management

Hi Community, 

I have two questions regarding unit of measure management. 

1. How can I add a new unit of measure that is not defined in the preferences for all magnitudes (length, mass, volume, area) ? Is it possible to customize a new unit of measure within the environment ?  

2. I want to edit unit of measures on case-by-case basis for continuous provided material and continuous manufactured material type objects. For example, I define m³ for continuous provided material (volume) in the first case, next case I want to define cm³ for the new continuous provided material (volume). 

I don't want to make a general definition, I want to make it specific to item.