It should be fine, if you're certain
Okay, this is an old stackexchange FAQ and unlikely to get any real attention, but to me, this rule seems needlessly punishing on new users, especially when the edit tool is perfectly capable of allowing users to help new users and then placing a comment to inform them.
For example, take this question. It was closed because of the lack of a system tag, even though it is obviously a question about fifth edition. Armor of Agathys is a Warlock spell in one, and exactly one, gaming system. In addition, their other question was also tagged 5e, so we know they're a fifth edition player. I added the 5e tag to help the new user and informed them in the comment, which would have allowed them to go "oh right, I forgot" and remember to do it themselves in the future.
Instead, the change was rolled back and the question was forced closed because they themselves didn't add the tag. This isn't a big deal in itself, we have closed questions all the time, but this feels needlessly petty. The idea that the original poster won't learn to use system tags correctly if somebody else helps them when they forget it once is ridiculous.
"Yeah, we could help you, but we won't" seems patronizing to me, and it results in perfectly answerable questions being closed. Other stackexchanges don't use this logic, because a good question with a missing tag is still a good question, and it can help other people even if the original poster never comes back.