Add A Saved Variable To The End Of Each RSS Feed Post URL

Good Day All.
Okay. Ive given it a shot for the past 3 hours and I just can't seem to find the spot, file, function, whatever it takes to add a piece of content grabbed from a URL and place it at the end of each RSS feed post.
Let me see if I can explain.

I have an affiliate site at http://shop.intimatetickles.com
The wordpress rss feed comes in at http://shop.intimatetickles.com/shop/feed

For my affilliates (about 60 at this time) they add to the end of the base url ?tickles= and their affiliate number, so the URL looks like http://shop.intimatetickles.com?tickles=17 for example.

I want my affiliates to be able to submit a feed. I also have a system that will drip post RSS feed items to social media, and I would like to give them use of this to post product pages to social media.

IF I ACHIEVE the task of add the affiliate code to the end of each product url obtained from the feed.

So I used $myaffid = htmlspecialchars($_GET["tickles"]);

which successfully grabbed the 17 (in my tests)

Now I need to figure out where, how to place the varaiable ($myaffid) so that each URL gets this added to the end of it.

I tried to write a function....
function add_aff_id($permalink)
{
return $permalink . $myaffid;
}
add_filter('the_permalink_rss','add_aff_id');

But this does not seem to work.

Any ideas?

Thanks in advance.

D. Storme