Customize fastener

[ltomuta]

I need a DIN 912 M4x18 Hexagon Socket screw. The faster library offers 16mm and 20mm versions.
I can insert the 20mm version, then Edit the component in place and change the length param to set it to 18. Save and the change is applied to all occurrences.

Also I can't change component's name/description to reflect the length change. If I do a "Save copy as and replace", it only replaces the current occurrence of the component, all the other remain with wrong name as they still point to the original edited component.

There is no replace component option for fasteners either. 

My assembly is now a real mess and quite possibly others are affected as well.

Is there a way to tweak the fastener generator and provide more granularity for some screw types as well as extend the min/max length limits?

[ltomuta]

It is worse than a mess, now I see that the Fastener library is not able to insert the 20mm version of the fastener in my project. It creates new components with "M4 x 20" in the name but does no create new file in the Fasteners project and instead xrefs the same edited file which now has the 18mm length.