How to create a script that makes the player able to change the states of objects?

Unity Engine
1

First of all I want to apologize in advance if I word some things wrong here, I’m very novice to this and couldn’t find a different way of conveying what I mean.

So basically I want the player to be able to touch something, then that something would transform into something else. If you want an exact showcase of what I am looking for please refer to the game de Blob (1 or 2).

I would figure I have to show what it would look before and after but I don’t know how I would go about doing that. Thank you in advance.

2

Note: If you watch showcasing of de Blob, I want to recreate the ‘painting buildings’ part.