Code Replacement

There's another option. If "MU1" has enough recognisable meaning to you, but you want other people to see the more useful "David de Gea", you can create "David de Gea" as an added synonym, for the keyword "MU1". Then in the Keywording panel you can change to "will export" mode to preview what keywords other people will see, when an image is exported to which you have added the "MU1" keyword.

That image does not have "David de Gea" applied as a keyword, but by virtue of that synonym, it will now show up when you text search for (e.g.) "Gea". And if you later remove that synonym from the "MU1" keyword, it will then no longer export or function for text searching of images.

Even thouh some time has past since you ask I'd like to share my fiddly solution.

I use PhaseExpress on Windows which monitors all keystrokes when running and replaces certain inputs. You can prepare replacement list similar as with Photo Mechanic. You can also limit PhaseExpress' monitoring to a certain application (e.g. Lightroom) and also do some more advanced stuff which isn't needed for this. 

Some aspects of the replacement (the way it is done) can be configured. Normally it don't tamper with some keys as ENTER etc. I changed this to also recognize some of them so that I could type a caption like "On the left: MU1[ENTER]" without the need for a comma, whitespace or other seperators that could mark the end of a replacement code. (PE basicaly sits inbetween the keyboard driver and the application and analyses all keystrokes while passing them through. With ENTER after a replacement-code its a little special - it first replaces the completed code before it sends ENTER to the application. This way ENTER acts as I like it: It signalises the end of a potential code to PE and after that it signalises the end of my caption editing to Lightroom.)

Main downside is: The replacement happens through tampering with keystrokes in two steps.

1. PE detects a code (MU1,)

2. By quickly sending virtual keystrokes PE undos the code typing (deletes MU1,) and then generates the intended text (David de Gea,)

It's really fast but you absolutly can interfere with this while it sends virtual keystrokes by accident. Lightroom don't know whats happening. It just receives the keystrokes. Imagine clicking somewhere which closes the caption field, while PE still sends some virtual keystrokes. Lightroom then will interprete them as shortcuts (e.g. instead of typing " Gea" this happens: [whitespace] opens the image, [Shift]+[g] opens grid view, [e] opens Library Loupe view, [a] does nothing – worse things could happen with other keys).

Nonetheless it seems to be the best way to add code replacement capabilities to Lightroom (or other applications). I just searched for a better solution myself again hopeing something has changed in the last one or two years. Haven't found anything better.

You can do the internet searching, but I believe that John Beardsworth has created a plug-in that will do a global text search and replace.

And where would you do this? Keywords?