I'm playing with a simple chat room program

What program? What protocols does it use?

I need the server to sometimes do nothing, ie not reply to a request. If I do this I get an error from Apache

Well, don't do that then, or get apache to ignore it, or something else

If I send a blank header the browser tries to download it as it's getting a non-executable file

A "blank header" is nonsense , apache is probably fixing the headers for you so they're not blank (nonsense) anymore ... apache documents this

can this in fact be done at all?

Sure it can, if you learn about the internet you'll know the magic words

$ perl -MCGI -e " my $q = CGI->new; print $q->header(qw/ -status 204 -
+nph 1/) "
HTTP/1.0 204
Server: cmdline
Status: 204
Date: Tue, 19 Nov 2013 13:58:00 GMT
Content-Type: text/html; charset=ISO-8859-1
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