a lyr is old binary ESRI code (ArcObjects) and FME has basic support for these
a lyrx file is stored as a JSON file, so it is possible to read it and adjust it. I suggest you open one and see how complex they are… as it stored more than just the symbology applied.
this idea has been proposed numerous times in the past
and this from 5 years… is telling me it was released 😀