Hello, I know this is a strange question, but I submitted a demo to a previous NaNoRenO in 2018 and haven't touch it until a few weeks ago. Could I still submit it with the intrenaimo tag or that would disqualify it?

If it was for a previous NaNo, it can't be submitted to a new one. But you should use the IntRenAiMo tag for yourself anyway! Hopefully we'll get enough traction on it that people will be able to search it.