I understand the basis of Royalty Free. There are some restrictions on items on other websites that are "Royalty Free", that say it can only be used 500K times and can have limits on how they can be manipulated?
For instance, you can download a Royalty free picture on a website, of a person. You can manipulate the photo making it black and white, enhance colours, or other basic changes, however you can't change it to give the person some sort of skin condition or disease, or change it to put in political, statements. Different websites can put in restrictions for their Royalty Free items.
So below is CGTrader's Royalty Free rules. I don't see a statement of being able to modify the model. Does that mean if it is not expressly stated, then it is expressly forbidden?
https://help.cgtrader.com/hc/en-us/articles/360015124437-Royalty-Free-License