Do you want to map a custom page to a different category or to different URL? There are two types of mapping which can be done to a custom page.
1. Create a custom page and map this to any other category from community admin.
2. Create a custom page and assign a different URL to this as by default custom page in lithium looks like this https://communityUrl.com/t5/custom/page/page-id/page-id. This mapping can not be done from community admin, you need to raise a ticket to lithium support for this.
Regarding the custom page Url for the landing page. Few suggestions
https://community.hubspot.com/Idea-home
https://community.hubspot.com/HubSpot-Ideas
