When I registered the ENS address which is similar or identical to an existing name, trademark or corporate name, can I sell it to a the company/individual having rights in that name?

Yes, could can. This is also the typical situation. The owners of the name/trademark/company name will likely want to settle with you and get their hands on the ENS domain rather than fighting you in court and then not even knowing where, how and when to enforce their rights against you. It does not mean that I encourage the domain grabbing business, because I most certainly don’t, but most likely, a deal with the interested owner will not create legal issues once settled (provided that the settlement makes that clear and includes a waiver).