The basic guidelines do not say you can't add more information within the Genre spoiler, and the tag list is woefully inadequate. Take a look at the
My Dorm Genre spoiler to see an example of what a good Genre spoiler looks like, with Planned tags, Never happening tags, and more detail about each controversial tag's status (avoidable/more clarification/etc.) This information can also be put in the Developer Notes spoiler, if the dev doesn't want to use the Genre spoiler for it for whatever reason.
As for partial harem vs true harem, as the writer I'd assume characterization and narrative is up to you. Generally speaking, I've never seen people who minded if an LI's characterization slips enough to permit sharing of an MC, other than aggressively anti-harem people. With a reluctant harem member (e.g. one who thinks "I don't want to share, but I'd rather share than not have anything with [the MC]."), it can even introduce some mild conflict dynamics that can occasionally be enjoyable. Hell, the default harem queen/enabler in
Sorcerer actively does not want to share, but she encourages it to strengthen the house.