Freezing boiled octopus
You can most certainly freeze some of it for cooking later. I have heard that this actually improves texture by tenderizing it. I'd suggest doing so in a freezer-safe bag with as much air removed as possible. Depending on portion size, lay it flat or in pieces that will be easy for you to portion later if you won't eat the rest at once. That will make it easier to use without having to partially re-thaw.