I want to change the title of a layer in a map legend, and I would ideally like to only change it in the legend without modifying it in the table of contents. If I have my symbology set to "Features - Single Symbol", I have an option of specifying a label appearing next to the symbol in the table of contents, which would change the label without affecting the layer title in the table of contents. But I don't have a similar option for any of the other symbology options - "Categories", "Quantities", etc. I'm aware I could simply change the layer title in the table of contents and it would modify it in the legend. But I'm using a map document which is accessed by a few different users and lots of different layers with similar titles, and it's important for them to all stay the same to avoid confusion, so when I'm producing lots of different maps I have to frequently change the title and change it back, which is inconvenient.
You can convert your legend to graphic. You then lose all links with the map and the table of content, which is what you want but could be ennoying if you change the colors AFTER converting to graphic element.
In practice :
1) go as far as you want to make a nice "linked" symbology and insert your legend items.
2) right click on the legend > convert to graphic
3) right click on the graphic element > ungroup (until the text is alone)
4) modify your text
For Categorized symbology you could change the header (by default it's the field name use for symbologie) then in the legend properties choose to display only the header and not the layer name this way the layer name stays the same but the legend display whatever you want.
For Quantities symbology I dont have a solution as ArcMap doesn't seem to allow you to change the default header.
One work around could be to expend the layer title with additional information (for exemple going from "My layer name" to "My layer name - Symbology") this way the layer is still identifiable in the table of content and the legend has the information you want added....