I dunno how you expect to rotate log files when you can only append to them . . .
That said, a simple # chflags -R 0 /var/log
should unset everything in there.
I suppose # chflags -R nosappnd /var/log
would work as well.
This is assuming you're not at a kern.securelevel>0, in which case you'd have to go into single user mode to revert.