Although it seems you have worked it out
I thought you might be interested to hear about my experience
with installing codeword protected HP-UX SW.
However, I have to admit that I never fumbled with a trial license.

Usually if you posses a codeword and customer ID
installation would be done by swinstall like this

# swinstall -v -x customer_id=XXXXXXXXX -x codeword=XXXXXXXXX -x mount_all_filesystems=false -s /path/to/sw.depot \*

This should install all filesets of such a depot.

Sometimes depots need a reboot (certainly not the ANSI C compiler)
if for instance a new kernel needs to be built and booted.
You can check in advance if a depot requires a reboot by issueing

# swlist -l fileset -a is_reboot -s /path/to/sw.depot

and it show either false or true.
For such a depot that requires a reboot the above swinstall would be aborted
after the analysis phase because the autoreboot flag is per default set to false.
To change this include in the above swinstall command another -x option of
-x autoreboot=true
swinstall would also abort if the filesystem size check would detect that the space
in the target filesystems wouldn't suffice.
In such a case you should check the ERROR lines from the output that are also
logged to /var/adm/sw/swagent.log which filesystems were deemed insufficient.
To check how much space would be required for a depot to install you could run

# swlist -l fileset -a size -s /path/to/sw.depot

and to see what files would be where installed you can issue

# swlist -l file -s /path/to/sw.depot \* | more

After the codeword protected depot has been installed you usually find your codeword
and customer ID being stored in this file

# cat /var/adm/sw/.codewords

As for the HP-UX ANSI C compiler its depot is on the application set of
CDs that appear at least twice a year.
You need to mount any of the CDs and inspect a file in the root of the CD
which usually is called CD_TABLE_OF_CONTENTS.
There you search for ANSI C where it reads the name of the depot
(something like B?????) and also tells you the install size.
Then page backwards up until you reach the CD delimiter that tells you
on which of the 4-6 CDs the depot is located.
To mount your CD you of course need to know the device file to access.
You can find out by

# ioscan -knfCdisk | more

Then

# mkdir /cdrom && mount /dev/dsk/c?t?d? /cdrom

and find your depot

# swlist -s /cdrom B?????

You could either directly swinstall from CD

# swinstall -x codeword=XXXXXX -x customer_id=XXXXXX -s /cdrom B?????

or first move the depot from CD to some filesystem on your box
so that you also could install over your LAN via RPC on other boxes

e.g.

# swcopy -x codeword=XXXXXX -x customer_id=XXXXXX -x enforce_dependencies=false -s /cdrom B????? @ /some/dir/on/your/box

Then you could install from another box on your LAN

# swinstall -x codeword=XXXXXX -x customer_id=XXXXXX -s your_depot_host:/some/dir/thereon B?????

N.B. the official website to get a codeword would be here

http://licensing.hp.com/welcome.slm

Very important, you need to specify the ID of the CD from where you would install
the depot (as been read from CD_TABLE_OF_CONTENTS)

HTH