The split infinitive: They could be more formally written as...
That's not a split infinitive, because it's not an infinitive at all.
The word rearrangement you suggest has null effect, except perhaps for questions of style.
The thing I don't like about "They could be more formally written as..."
is that it's in the passive voice. This could be eliminated by rewording as
"One could write them more formally as..."
But, of course, there are contexts in which passive voice is not only acceptable
but preferable, for example, in scientific writing. Is this discourse scientific
enough to merit passive voice? I don't know, but I personally would err on the
A word spoken in Mind will reach its own level, in the objective world, by its own weight