Sometimes the agent's standard item keys (e.g. "vfs.fs.discovery") are not fully sufficient. So you can use a custom script using a custom item key to serve the information.
But in some situations it would be easier to still use the same item key. Unfortunately if you configure the item key in the agent config the agent complains about a duplicate key:

ERROR: failed to add UserParameter "vfs.fs.discovery": duplicate key

So it would be helpful, if the agent's standard item keys could be overwritten with the manually configured one.