As it says under HELP CRTL Feature_Logical_Names:

      o  Do not set C RTL feature logical names for the system.
         Set them only for the applications that need them,
         because other applications including OpenVMS components
         depend on the default behavior of these logical names.

The same logic applies to setting them for a process which is used to
run multiple applications.


> For some applications [...]

   Define/describe "some applications".  If you build the things
yourself, then it's relatively easy to add code within an application
to set these things, which avoids interfering with other applications.
Setting DECC$ARGV_PARSE_STYLE early enough is a little tricky, but even
that's pretty easy for a plain C (not C++) program.  The Info-ZIP UnZip
and Zip programs do it, for example.  (If anyone knows a simple recipe
for getting a user-supplied LIB$INITIALIZE function called in a C++
program, I'd be interested.)  Others, so far as I know, can be set at
any convenient time.