Oops - sorry. I should be reading those posts more carefully 8-(
I don't know too much about OSDD's macro language, but the CREATE_DIRECTORY command might do what you need for directories. If the directory doesn't exist already, it will create it, otherwise issue an error (which you can probably catch using TRAP_ERROR).
For files, OPEN_OUTFILE with option DEL_OLD might do the trick.
Sorry again for the misunderstanding.
Claus