[cpp] Replace 'could' and 'might'

as directed by ISO/CS.

Author: jensmaurer

source/preprocessor.tex

@@ -1680,8 +1680,9 @@
 The macros defined in \tref{cpp.predefined.ft} shall be defined to
 the corresponding integer literal.
 \begin{note}
-Future revisions of \Cpp{} might replace
-the values of these macros with greater values.
+Future revisions of \Cpp{} will replace
+the values of these macros with greater values
+when the corresponding feature is modified.
 \end{note}
 
 \item