What do you exactly mean with "not limited icon"? If you don't know the exact word for it, maybe you can create a screenshot showing what you mean and showing what you want.
When should this "not limited icon" exactly change? After a certain fixed interval? After random intervals? After some events?
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I think you mean the display picture. In this case, browse the
scripts database in the category "
Display Pictures".
There you'll find some scripts which can change your display picture automatically after some intervals. Most notible:
Display Picture Changer.
Download that script and install it by double clicking on the downloaded file. After it has been installed, you can set it up by going to the Plus! script icon (above the contactlist) and selecting the "Display Picture Changer" menu.