The short answer is yes you can do other treatments but the treatment will depend on if it’s a local (still stage III) or distant (stage IV) recurrance.
As you know, other than surgery there’s really only Interferon (and maybe radiation depending on the location) out there for stage III as standard treatment, however, there are some limited trials for stage III patients using other treatments, for example IPI (Yervoy) and some of the Braf inhibitors.
My understanding is that Interferon would count as one “systemic” treatment for trial qualification purposes. Some trials limit the number of systemic treatments you’ve had but this should not be an issue relative to a recurrance since interferon is not very effective and the treatment would have been considered a failure. The only other possible trial entry issue would be if your last injection was fairly recent, like less that 3 months ago.
Hope this helps and you stay cancer free(!!)
Jeff