Hi,
In generally, from metadata are important only “name” and “description”. Most important (for me) are “Attributes” in Components, and “Assigned package” in Devices.
I try to explain my idea.
Situation 1.
I create my resistor library and I use each component/device for each resistor part number (yes, for each value I create a separate component and device). In attributes I add fields as “Manufacturer Part Number”, “link to datasheet”, and order numbers for some suppliers (Farnell, Mouser,…). This is preparation for BOM export also 
Situation 2.
Resistor library is created with all E24 values for package thru-hole radial RM 7,62mm with MPN and order numbers. Now, I need add to all, a new package variant for RM 10,16mm…
Situation 3 (little bit utopia).
Resistor library is created with all E24 values for package SMD 0805. Now, I can create a library for SMD 1206 packages… (yes, this require duplicate new library from existing one with new UID generation… maybe in future ) But after duplicating, I can change all package through mass edit to 1206.
And also library report can be done by mass edit.
And more…
I know, this mass edit is not easy to implement if we can apply all described situations. But in future, this canm be easiest way to manage libraries. Important is retain excel’s fields functionalities (move, copy, rows filter, cols hide/unhide,…)
Remember, good desing starting from good libraries!
AD. librepcb-parts-generator: I not tested yet. This is python scripts and I not familiar with this snake. Parts generator, should be integrated as function of LibrePCB.
AD SCH/PCB Property editor: Yes, yes, yes, and 100x Yes!
But please, don’t forget to edit property also for multiple selected objects (only common properties of course).
Regards.
Ed