[Magnie]

Well... you will need to replace ':EXTRAFEED:' with:

$article_content = $article_content.$extrafeed;

Otherwise you might need to put it in 'functions.php' where it loads the variable. I'm not fully sure of what you want though, sorry.

Or where you have ':EXTRAFEED:' have:

$efeed = getextrafeed()

$article_content = $article_content.$efeed

which should get the returned variable. :)