Clive: custom properties are meant to define properties that are not already available in QCAD.
For example, in a city map in which each house is represented by a polyline, each such polyline could be assigned a custom property 'house number' which indicates the house number of that house. This way, additional information can be added to a CAD drawing in a way that is suitable for further processing in databases, etc.
If I understand you correctly, you are more looking for a tool to copy attributes or properties from one entity to another one. I think such a tool to copy custom properties from one entity to another would absolutely make sense.
Perhaps like this:
- Select some entities
- 'Edit' - 'Copy custom properties from...'
- Click source entity to copy custom properties from
A similar tool could exist for attributes such as color, line type and line weight ('Edit' - 'Copy attributes from...') - is that what you had in mind?