I used SmartProperties but I put the concatenation directly in the basic "PieceName" field from the custom properties (See Attached File).
The only "problem" is that after filling in my fields in the Custom Properties tab (on the right of the screen), I have to open Smartproperties and validate with the checkmark for it to be taken into account.
Thank you all for your answers, they put me on the right track.
My problem is that I need the custom properties to automatically fill in the already existing plan blocks and bills of materials, but not everyone in the company (we are a very small entity) has SmartProperties.
If that changes, I'll certainly go through it but for the moment I can't.