Ok, here's an update!
Good news: my rat fur can be cleaned and saved!
Bad news: there is no fast and easy way to do it, it is a long and labor intensive process.
So far I tried different techniques over the 'test area' with the most severe shedding.
1) Initial dry vac to remove the most obvious shedding and dirt - not effective at all, but I started with this step anyway.
2) Wet vac with upholstery attachment. No shampoo, just a tap warm water. Removed a lot of the loose fibers and dust. Also washed away all detergent residue (which I believe was the cause of the shedding to begin with). After this step headliner looks like new and became nice and soft to the touch.
3) Blowing rat fur with a blowgun and compressor. Slow and boring process (I have a small 6 gal compressor and have to wait for it to recharge every 30 seconds), but it seems to remove pretty much all of the loose fibers and shedding. After this step shedding finally stopped.
4) Additional dry vacuuming clean up. After using a blowgun, there is a piles of loose fibers everywhere on the floor.
Now I have a proof that shedding rat fur can actually be cleaned, so I'm thinking about either finishing the cleanup myself (would take a few more hours) or just drop my Scamp
at the nearest detailing shop and ask them to do the job.
Anyway, I'm really happy that it looks like I can avoid rat fur replacement