To do it fully manually, which is what you’re going to need for custom names, you need to find images, and manually copy them to /home/pi/.emulationstation/downloaded_images then edit the xml files in /home/pi/.emulationstation/gamelists. Make sure to quit elulationstation first, or it will overwrite your changes.
Unless you mean simply using the scrapeer in ES and approving conflicts, but that’s not going to allow you to easily have custom names on the gamelists.
Another route, would be to scrape the games via Selph’s scraper, then get the missing info via the ES scraper, and once you have all of that, edit the incorrect games metatdata from the select menu inputting the name you want. Either way, if you want custom names in your gamelist, you need to do it manually.
^^ my other hobby