I think I understand the question. dgame wants to know if there is a pattern that can be loaded into a layout's text fields which == the string corresponding to the next or previous gamelist.
I don't believe there is. The closest thing is in definables, but this matches against aspects of the current ROM, not the current list.
In Mala » Options » MAME config » Pictures and Videos, you can set what MaLa looks up what image to display in the layout's "definables" regions. The default is "ROM", meaning that MaLa looks in the specified folder and displays a picture with a filename matching name of the ROM currently highlighted in the gamelist. I use this to pick up the screen orientation and controls, eg. "vertical" and "8 way joystick" in my layout shown below.
This can be changed to "ROM +1" or "ROM +2", which might be handy if you wanted to show the snaps of the games above and below the current one, perhaps in some sort of 'snaps in scrolling window' device or something. Was playing around with a layout that employed this a while back.