Just a bit of caution though. You could use a parked domain as a temporary domain, but when you do with the objective to have it changed, you can't use it to rename your main domain, you will have to remove it first. As the cPanel system would then see the domain is already registered in the system. So probably better to be a little patient until someone has changed the main domain name for you as I have done earlier.
Also note that parked domains are not indexed by Google in the same way as main domains. So it is always better to keep your main domain your main domain. Here's a tutorial about why parked domain is not always a good idea if you are using it for your main domain.
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I'd say have your main domain always your main domain. Then for other domains, add them on so they all have their own root directories for Google to index. Then parked domain is to point other domains to the domains you already have. Many companies who want to beef up their marketing use the double domain thing. I.e. have parked domains directed to their existing domains or add on domains.