While you probably could reverse a double ended dildo, it won't be ideal. They are designed so that the shorter end goes in the giver. If you reverse it, it will probably be too sort to use for pegging and will result in a frustrating experience.

Instead, I would suggest using two single dildos base to base. You should be able to insert a dildo of your choice into yourself, and adjust another for your partner in a harness and position them so the bases push against one another. When selecting a dildo for your partner, be sure it has enough length or else the dildo will come out easily and make for a frustrating experience. Hope that helps.