Editing into the facebook account isn't allowed from the phone's people utility. Is there any tool or trick in windows phone that can let me do this? Would be great to know. Thank in advance.
As far as I know, you can't do that. Unlike Google Contacts or Outlook.com People, Facebook isn't an address book, you can't add arbitrary contacts or change other people's information there. This isn't a limitation of Windows Phone, it's simply how Facebook works.
I suppose you could get around this by registering fake accounts with the names and contact data you want, then adding them to your friend list and syncing to your phone, but that's pretty inconvenient, plus might be considered impersonation and thus illegal (not to mention the actual person in question might not take kindly to that sort of thing). So really, just use your Google or Microsoft account for storing contacts.