They are the only nuisance one cannot turn off in sandbox mode... I know not to accept Nostros, so the trouble is most likely restricted to Memaus infecting peeps.
From your link here you can adjust the
mood_in00.txt to make Skrashers less of an issue.
Find the default mood, MOOD_INC_DEFAULT and set the body value for
(Spawn) to something like
-8000. They'll lose health at a massive rate.
Find the mood entries MOOD_AT_BIRTH and MOOD_AT_BIRTH2 and set the
body value for
(Spawn) to about 500 in each case. They'll spawn with almost no health. The two values represent a min/max for random selection so setting them both low is vital for this trick to work.
Skrashers spawn with a tiny amount of health that fades away almost instantly so they die straight after appearing...
I've not actually tried this as I don't want to try and find and install the game, but this answer is based off previous experience (it was like 8 years ago now though..) and from browsing through my mods in my old file archive and looking over the files I've kept in there...
I'm hoping it's pretty accurate.
Not a real answer to your question, I admit, but they've never been a real problem for me.
Just build lots of Scuzzers Mk II or III (really cheap after researching them properly) and a Recycler every few sections. With the e the Recycler extracts from the garbage, they pretty much pay for themselves.
Also place lots of Litter Bins, in particular next to everything that produces garbage.
I found the MEMAU_TARGET_LEVEL setting, described here, but still sometimes Skrashers show up.
If you place all buildings that generate garbage on your entertainment deck, this isolates rats to that deck. This means all din-o-mats must be placed on the entertainment deck. No garbage on the engineering deck means no rats there; and since Memaus and rats don't move from one level to another, the Memaus stay on the engineering deck and the rats stay on the entertainment deck. You may see the occasional tourist drop litter on another deck after buying something and using a lift, but placing garbage creating buildings (shops and food sellers) far from the lifts and putting trash cans close to them reduces litter on the engineering deck to almost nothing. Isolating Memaus and rats from each other means no scrashers except for infected from the Nostros.