If you secure your entry into an event via the Great Run website, you have your own place.
(If you secure an entry into the Great North Run by being successful in the ballot, you also have your own place)
This means, you do not need to raise money for charity. Or if you did, you don't have to raise money for the associated charities listed on the entry form or website.
You can raise money for any charity/cause of your choice. All you need to do is contact your chosen charity directly and request sponsorship details.