You could play an in-game match of Pokemon in which players agree to interpret the win and lose states the opposite way around. However, such a game would be very unlike Suicide Cup in that the optimal strategy would be to attempt to forfeit before the other player in order to trigger the loss state. Or perhaps it could be argued that Suicide Cup could be simulated by players agreeing to ignore the 3DS game state in this situation...but this seems to violate the idea that the meta can be played in-game. In principle, it seems that any OM could be considered as an UM in this way, by players agreeing to ignore the in-game state to differing extents and manually calculating the outcomes of decisions under the OM rules.
This might seem like irrelevant hair-splitting, and I would be overjoyed if that were the case. However, as according to previous answers, metas reclassified as UMs can no longer be nominated for OMotM, the classification is unfortunately highly consequential because becoming a UM seems to be functionally a massive 'downgrade' for a meta at this time. May I ask if there has been consideration of harmonising the relevance of OMs and UMs, for example by running an 'UM of the Month' event similar to OMotM?
I won't be speaking on UMotM, as I honestly have no idea if such a thing is possible at any point in time, but I'll speak on everything else.
Balanced Hackmons, Almost Any Ability, Mix and Mega, Sketchmons, Camomons, etc. None of these OMs can be played without hacking or using third party devices, regardless of what deals you make with your opponent. Meanwhile, looking at UMs:
Anything Goes is simple, just do whatever you want.
ZeroUsed is just a list of bans, so it can clearly be played by talking to your opponent.
1v1 is an agreement with your opponent to play a 'bring 3, choose 1' meta, which is fine.
LGPE is an agreement to play on LGPE.
Mediocremons and Middle Cup both just have banlists, though MC is played at lvl 50 as well. Again, this can just be done by agreeing to it with your opponent.
And that brings us to Suicide Cup. Sure, the agreement here is a little more complicated, but really only a little. 'Whoever loses wins, unless you forfeit'. As someone who doesn't play SC, I'm fairly certain this is what the meta comes down to.
As to whether or not UM is a downgrade, as a leader of one of them, it is very much not. Granted, I lead ZU, a level 2 meta as opposed to a level 1 one, so you can argue that that's not fair. I understand the concern regarding no UMotM or LC for them, and maybe it was a downgrade in that sense, but none of these have won OMotM in a long time (maybe SC but I don't think so), so honestly giving them a clearer route and goals to grow to is probably better for them, even if Level 2 is still way out of their reach at the current time. Meanwhile, new UMs will have an easier time getting accepted, while this was incredibly difficult to do before. ZU, for example, existed for years before we were accepted as an OM, whereas if we had had UMs back then, it'd have gone much smoother.
I hope this answered your questions