Nothing to do but for Colorful Arty to update the styles so that no problems occur in v12.10. In the meantime, it's like you said, just play it in 12.8.
Also:
Just a friendly reminder that level fixing should be left to the pack author(s). I'm sure your effort in a potential fix for one of the levels is appreciated, but we're not mind readers and hence we don't know if that's really what Arty intended. You can suggest fixes verbally, that's fine, but our time and energy is better spent elsewhere, and ultimately the responsibility is on the author, aka, Colorful Arty, to maintain the pack/level fixing. For everyone else, we just play the packs that the author releases and should simply respect the authors by not messing/editing the levels of their packs. The pack is, after all, the author's property. Why worry about something that's not our responsibility? Fixing the levels themselves is the least of our worries and should be left to Arty to take up since they're his. Even if it appears that backroutes won't be fixed, you never know. Sure, the fact that there hasn't been any follow-up posts since the release from Arty can lead you to believe that, but it doesn't mean that he won't do any fixing. He still might. Finally, he's still active here, even if he's not on all the time.