how to merge categories from different feeds? | CyberSEO Pro | Support Forum

Helllo

I have 2 rss feeds which have different categories name, example

Feeds Site A | Category name: Spicy Food

Feeds Site B | Category name: Sweet Food

I want to combine those categories into All Food. I tried some php code, but no luck

if ($post['categories'] == "Spicy Food") {
       $post ['categories'] = "All Food";
}

Can you help me? Thank you