Pete, from experience I can tell you that the only success I had with “re slinging” was to go back to sqaure one and reflash..
I ended up re flashing with a windows sercom program with the original Linksys formware (available at their site).. then I flashed the unslung 6.8 using the upgrade feature, and un slung the Slug.
Perhaps the re flash to stock was unnecessary, but it worked for me.
Dave