In this sentence here, I understand the overall gist of what it is saying, but I just can't find any sort of definition for ネタ. I'm thinking its some kind of slang which requires a bit of contextual knowledge of the word in order to understand it in this case:
その前は『生きた心地がしない戦線』だったわ。完全にネタだったから一日で変わったけど
My guess is that it is expressing the speakers ridicule with the previous name of the group
Relevant definitions of ネタ here are
４ 演芸で上演する作品。また、その内容。芸の種類についてもいう。「落語の定番―」「歌―」
５ 人をかつぐための、真実めかした作り話。悪意のある嘘ではなく、相手を笑わせたり軽くからかったりする程度である場合をいう。「彼の失敗談は―だろう」
4 means a piece of comedy (performance) and 5 a fake story for laughing. The usage in question is mostly 5 even though it is not exactly a fake. A relevant phrase is お笑いのネタ, literally meaning a seed of laughing
So you are basically right. It means Formerly it was called .... The ridiculous (joke) name was changed in a day.
