If you want to be clean you can use the finish method on the XML::Parser::Expat object:

finish
           Unsets all handlers (including internal ones that set context), but
           expat continues parsing to the end of the document or until it
           finds an error.  It should finish up a lot faster than with the
           handlers set.

Generally, when using XML::Parser, it is worth reading the docs for XML::Parser::Expat, as a lot of very useful methods are only described there.

There doesn't appear to be any express support within XML::Parser for interrupting the parse. I would suggest you consider employing an exception to stop the parse. Consider the following code. Also think about using the Exception::Class to further clarify that the parse is being interrupted for valid reasons instead of depending on a text message in the $@ variable.

eval { $p->parse( ... ) };
if ($@ =~ /^Interrupted parsing/) {
    # The parse was stopped early.
}

sub whatever_handler {
    if ( $found_record ) {
        die "Interrupted parsing";
    }
}
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