for a once off, perhaps do it just using bash style shell. if you have access to any unix system log into that, else if on windows, either install cygwin bash (or figure the conversion to powershell) or maybe easier use perl/python
if you have a file of mac addresses, like this
$ cat macs.txt
00:11:22:33:44:55
11:22:33:44:55:66
aa:22:33:bb:44:55
then use a one liner to generate the CLI commands, like this
$ for i in `cat macs.txt`; do echo "stm add-blacklist-client $i"; done
stm add-blacklist-client 00:11:22:33:44:55
stm add-blacklist-client 11:22:33:44:55:66
stm add-blacklist-client aa:22:33:bb:44:55
$
here is a perl version to achieve the same
c:\temp> perl -ne 'print("stm add-blacklist-client $_")' macs.txt
stm add-blacklist-client 00:11:22:33:44:55
stm add-blacklist-client 11:22:33:44:55:66
stm add-blacklist-client aa:22:33:bb:44:55
c:\temp>
now copy and paste them into the CLI of the controller, perhaps 50 lines at a time.
hth