In this example I'll change commentary name of one of my player from youth academy to Messi. Tested only for english commentary, may not work for other langauges. You can find the IDs in FIFA 20 IDs sheet in "Commentary" tab.

Editing player commentary name through GUI

1. In game go to squad hub and hover the player (W.Henry in my case)
2. In Live Editor in GUI click on "Players Editor" button and wait until it will load player data
3. To change player commentary we need to change his "Last Name ID" You can find the ID in FIFA 20 IDs sheet. Copy the value from "nameid" column, put it in "Last Name ID" in Live Editor GUI and press "Apply Changes" to save it.
4. Done

Editing player commentary name through cheat engine

1. In game go to squad hub and hover the player (W.Henry in my case)
2. In Cheat Engine navigate to "FIFA Database Tables" -> "Players Table" -> "Player Info"
3. To change player commentary we need to change his "lastnameid" You can find the ID in FIFA 20 IDs sheet. Copy the value from "nameid" column, put it in "lastnameid" in cheat engine.
4. Done