There are a couple of different ways you can go with for your questions #1 and #2.
But, would like to know more details on what exactly you are trying to do so I can recommend the best method
1) Custom post filtering how exactly do you want the Users to filter and sort?
A custom page with search and filtering options?
Or a Widget that they can filter with?
Do you need them to search with data contained with in the actual posts?
Or just with the keywords and Categories attached to posts?
Can you give an example of how a user will use the filtering?
In your example of Recipes sounds like you wanted to have deeper levels or "sub-categories" / "Grandchildren Categories"
Post Category: Recipes --> Bread, Cookies, Meats, Deserts, and etc.
Bread --> Whole Wheat, White
Cookies --> Chocolate Chip, Sugar, Peanut Butter
Deserts --> Cakes, Cookies, Ice Cream
Is that correct?
2) What type of "transformation" do you need to apply to a post before it is served?
A. Design/Graphic wise?
B. Data Transformation where you add additional information or take away information from a post?
I know you want to keep the "original" post as-is and just make some "temporary" changes to the post for users to see.
Does this transformation applies to all posts and users or to just some posts or /and users?
If you have a live version of your site can you post the URL here or PM me with the URL?
Seeing a website and your ideas can go a long way in figuring out what needs to be done :)
Have a great Day!