"What are you trying to filter out? You're already in the forum.
What is the format of the URL of the threads. If it is just showthread* then
there is no way to filter out thread of other forums."

I want to filter out/exclude links posted by users inside their comments or
signature that redirect to other threads inside the same forum because they
get caught by my filter rule and make httrack escape the subforum I specify
him and downloads threads in other sections I don't want. 
So in other words I would like httrack to only grab links which are part of
the page structure: threads' main links and threads' pages links. 

Format is www.<forum>.com/showthread.php?t=<threadnumber> So for example, say
I target a subforum (www.<forum>.com/forumdisplay.php?f=<subforumnumber>)
which contains threads=t=4,54353,49943,288; then httrack will work as expected
and downloads those threads numbers and their respective pages only but if
while exploring it finds in the user comments a link using the same url that
redirects to the present forum, then he caught it and escapes on wherever that
link leads him, thus downloading many unwanted parts of the forum.