How can I fire a custom function just once in Woocommerce - php

Question

I need to add variations to my Woocommerce products programmatically and I borrowed the code from this answer thread:
Create programmatically a WooCommerce product variation with new attribute values
It works, but gives me two variations when I pass this data array:
$variation_data = array(
'attributes' => array(
'kidssize' => '2'
),
'sku' => '',
'regular_price' => '120',
'sale_price' => '',
'stock_qty' => '',
);
My guess is that funcntion fires two times.
Since i am a noob in php and backend in general all I know how to call a function is from some template file and visiting the page.
And to prevent other visitors from triggering it I use
if(isset($_GET['**parameter Only I know**']))
… wrap and call it going to the page with set parameter;
I understand that this is a really bad way for doing that, but how do I do it otherwise if I need to call function once and never use it again?
And is even firing twice a problem here or is it something wrong with my array?
EDIT:
Here's a detailed process of what i do:
i put the function from the link above in functions.php,
then put the call in footer.php of my theme with above mentioned wrap (the parameter is irrelevant - it could be anything, because it's just used as a trigger)
and go to the page with said parameter to trigger the call,
load the page only once and look for the result in admin panel.
And it has 2 variations always, even if i add more attributes to an array it will return 2 variatons of the last attributes array item;