To edit the default GDmenu vmu icon when in GDMenu simply go into the Assets/VMU folder and inside you will see two text files, One is the default ascii art and one is mine like you see in the picture above.
I recommend opening one of those text files with HxD and clicking on View and then click Bytes per row and change it to 48 then on the Decoded text section you should see the text icon you're looking to alter and once done save it under a different named txt file.
Once you have your txt file made simply go to Advanced Settings on my app and click Customize Options and open up your VMU Icon txt file and it will apply it, You can also see a preview of it after it's applied by clicking the preview button.
On the VMU screen it will look different to the preview, Where you see # will be blank and where you see spaces in the preview you will see black text.
Had some people say some of the menu's were cut off for some reason so now you are able to manually resize them if that's ever an issue for you.
I have also replaced the optional 'GDEMU Games List Generator v1.3' with 'GDEMU Games List Generator v1.3 Mini' which is just a smaller version of the original again for similar reasons of some people saying some of it was cut off for them.