I thought I'd posted this earlier, but I don't see it now.
!testing:#eggfriedcheese:
var %match $+(!,$2,:,$chan,:)
var %match $read(additionalcommands.txt,nts,%match)
if (%match != $null) write -dl $+ $readn additionalcommands.txt
Note that, as I mentioned earlier, you should use the 'n' switch if you need to avoid a command containing $word_beginning_with_dollar being evaluated as an identifier. On the other hand, if you want to have a command containing $me or $nick then having those evaluated as identifiers, then avoid the 'n' switch.
The 't' switch only comes into play when line#1 in its entirety is a number, in which case mIRC sees that number as if it's the number of lines in the text file when searching for a random line, but it apparently doesn't have an effect on the 's' switch.