Is this actually their full name? I'd say it would be similar to saying that NEGA's band name is ネガ 04200921580406177042. Anyway, I guess either way is fine. I'm not sure how to change it myself but 大日本 is always read Dai nippon/Dainippon btw.
IIRC they made a post about it when they changed their name and specified that, yes, it's their complete name, but you can still just pronounced it "Gossip." Or something like that.
oh no @ using their full name
Breaking: vk.gy to rename to dainihon onitanjigumi akudoukai ni senkyo sare vk.gy.