CL Programming - commands with a list of like values

A question about simple basic CL Programming:

In a CL Program you have a command:
CPYF FROMFILE(&FILEA) TOFILE(&FILEB) FROMMBR(&FROMMBR) TOMBR(&TOMEMBER).
This works fine even if the value of &FROMMBR is '*N' - indicating that no
specific value is given for FROMMBR()

However:
CHGLIBL (&LIB1 &LIB2 &LIB3)
will not take '*N' as a value for &LIB3 but answers CPD0073. Neither will it
take blanks for a value (CPD0078). In other words: There is no way to tell
the CPP of CHGLIBL that the list contains only two elements. With &LIB1
&LIB2 &LIB3 it insists of getting three valid library names.

With commands as simple as CHGLIBL it's easy to build a text string
(containing as many blanks as you want) and give it to QCMDEXC, but with
more complex commands it would be nice to use the command directly, and not
have to build it in a text string. Is there a way to code varying number of
list elements in a single CLP command?


Henrik