There are a couple bugs with Slip that I am now aware of. But... that I can't yet provide a proper fix for. The reason being is that... since there were no reports of issues... I felt it safe to start making significant changes to the Slip code. So compiling any new build would be a major update. And frankly... the direction of the project itself has shifted. As for that topic...
Both Slip and the Custom Hiyoko NSP builder will be merged into CaVE. The next build of either will be... THAT.
But that CaVE update is still in progress to the point that I would not even announce it now if not for these bugs.
On to the bugs and the workarounds.
Bug: "I added a custom ROM, but Sloop+ crashes when I try to boot it."
Cause: Slip incorrectly sets the name of the ROM when importing it.
Workaround: Right click the game line of the new imported game in Slip, and select "Open Game Title Folder". Rename the .gba file to exactly the same name as the .sav file, except for the extension of course.
Bug: "I selected a new image for my custom ROM and its not showing up in Slip or Sloop+."
Cause: I forgot a slash, and the image is copied with the Sloop+ folder name as part of its name in a parent folder instead.
Workaround: Right click the game line of the new imported game in Slip, and select "Open Game Title Folder". Manually copy in the png format image and rename it to Title.png, overwriting as needed. You may need to close Slip first.