Can a 1S BMS be used for a parallel arrangement of 4 Li-ion batteries?
As far as LV cutoff is concerned. OK
But for CV cutoff to say 5% of CC with 4 cells sharing current, each cell must go to 1/4 of 5% CC to trip the CV cutoff. This extends the aging time during CV.
So if you can reduce CV from 4.2 to 4.0 that might be better as it will spend closer to the same time charging the higher ESR double layer charge as 1 cell.
Otherwise the CC rate will be shared and thus take 4 times longer from 3.8 to CV levels.
Consider the simple equivalent cct as C*ESR // C/x * ESR * y  so the secondary charge time constant ought to be the same as for 1 cell to give an equal compromise to longevity vs storage capacity.  Where x,y are variables of the double layer charge effect that causes the effective memory when you change the CV instantly then shortly after remove all charger or load and it restores back to nearly the same previous voltage.
In Short (no pun) it will work but I recommend you tweak the charging profile.. Max CC and reduce CV
The only other factor is does the BMS actually measure battery current or just charger current? If the Latter, beware of overextended CV times during load &gt; I cutoff.