Long story.... but summarise, I created some custom metadata fields for my own use. With hindsight one of the field names I chose was a bad choice I called it "client" and in reality most of the time I've been storing different information about a job in the field the name "subcategory" would be a much more appropriate name for how I use the field. Is there any simple way to rename a previously defined metadata field and still retain the data it is holding.
Here is how the field is currently defined
id = 'Client',
title = "Client",
dataType = 'string',
searchable = true,
browsable = true,
Adobe will probably step in and answer this; however, if it cannnot, simply add the new field names a new fields and write a routine to copy the date from the old field to the new field. Then when you are comfortable that it indeed was copied for all the images you are concerned about, remove the old field name.
Hope this helps.
Just go into the Metadefinition.lua file and rename the TITLE field to be whatever you want it to be but leave the ID field alone. Then be sure LR reloads the plug-in the next time you start LR. The displayed name will change on the metadata panel in LR to whatever you put in the Title field....