Hacking an existing plugin: modifying a string?

I’m trying to hack the JournalPress plugin, which hasn’t been updated in something like two years, so I can’t really expect any support on that end.

FYI, JournalPress is a crossposting plugin, which I use to crosspost to my LiveJournal. My issue is that I keep all the important content to be crossposted in a variety of custom fields using a custom panel developed in Magic Fields. I never enter any data in the_content if I can help it. JournalPress, obviously, is specifically designed to crosspost the_content.

I need to hack the plugin to declare that a series of custom taxonomies and fields are to be crossposted instead.

Here are what I assume are the relevant bits of code I should be paying attention to.

journalpress/lj.class.php

$params = array(
        "username" => $this->lj_userid,
        "auth_method" => 'challenge',
        "auth_challenge" => $this->lj_challenge,
        "auth_response" => md5( $this->lj_challenge . $this->lj_md5pwd ),

        "ver" => $this->protocol_version,
        "lineendings" => $this->lineendings,

        "itemid" => $jdata['itemid'],
        "subject" => $jdata['subject'],
        "event" => $jdata['event'],
        "year" => $jdata['year'],
        "mon" => $jdata['mon'],
        "day" => $jdata['day'],
        "hour" => $jdata['hour'],
        "min" => $jdata['min'],
        "security" => $jdata['security'],
        "allowmask" => $jdata['allowmask'],

        "props" => $jmeta
      );

"subject" => $jdata['subject'], is the important bit.

journalpress/jpfunctions.php

// The filters run the WP texturization - cleans up the code
	$jdata['event'] = $the_event;
	$jdata['subject'] = apply_filters( 'the_title', $p->post_title );

I have successfully modified this bit of code to make the contents of one of my custom taxonomies crosspost with $the_event:

// The filters run the WP texturization - cleans up the code
	$jp_custom_taxonomy = get_the_term_list( $p->ID, 'custom_taxonomy', '', ', ', '' ) ;

	$jdata['event'] = strip_tags($jp_custom_taxonomy).''.$the_event;
	$jdata['subject'] = apply_filters( 'the_title', $p->post_title );

Alas, I cannot add if/else statements to this particular line of code and the display I require needs an assortment of if/else statements.

I’m self-taught through trial and error when it comes to php, so I still have a lot to learn and my coding vocabulary is somewhat limited. I presume $jdata['event'] = $the_event; is called a string declaration? And if statements cannot be declared in a string? If that is true, there must be some sort of workaround? How do I add the results of if statements to the$jdata['event'] string?