Word wrapping is done by the OS functions thus the decision as to what it considers viable place to break the line is up to the OS.
You probably can replace the dash with $96$ which I don't think the OS will break on.
However I should mention that the latest PxPlus 2018 which use some newer Windows controls does not do a line break on the dash -- older version of the Windows controls do.
LET ml=10
MULTI_LINE ml,@(10,10,11,10)
LET ml'value$="Blue Widget 35-7/8x79-3/8"
So as mentioned -- its is up to the OS components as to if the break will occur. And to make this more confusing when running in iNomads Chrome does break at the dash but Firefox doesn't.