Some mods come as table decorations, which becomes bothersome.
So, how can I turn them into rugs?

There's a rug tutorial at http://bwsost.woobsha.com/JendRugMog/rugtutorial.html. If you're asking a question like this, I'm guessing you already know how to import the functionality from one object into another.

Sorry, the title of the post was't completely clear

It is about how to turn a hacked object, which goes on a table, into a rug

You'll have to change the base. You can clone the size rug (or rug-based object) you need (i.e. 1x1, 2x1, 3x3, etc) and import your object's sprites onto that base. Keep in mind that you'll probably have to fix the alignment of each tile (if multi-tiled) to get them to match up correctly, and that you will lose any functionality the original object may have had - without further editing, at least.

It depends on the object, but it would easier for me to add the new functions to a rug. Since rugs don't have their own functions they are good bases for adding something, though I usually prefer to use paintings. In any case it's hard to say something without seeing the object.

I'm talking about modifying an object to allow Sims to walk on it, so it doesn't get in the way.
Although the ideal would be to be able to place it in the same slot as any other object