I want to make a spell that gives units owned by a player to P12 so they become neutral and do nothing, but just wondering, are ups from the previous player carried over onto P12? Does that mean a unit with 4 armor will still have 4 armor after changing players? Or will it be the default of P12, 0?

I'm almost certain that the upgrades will change to the player that owns the unit. Tech will transfer though.

Only the range/speed/mana/sight/capacity upgrades and the reaver damage upgrade should be shared afaIk.

the standard armor and damage upgrades aren't shared while giving.

I very much doubt this as it's a weapon upgrade and unlike other techs it has 255 tiers.

Upgrades that don't default to a maximum of 3 can be shared, including reaver damage. All techs are shared. This includes upgrades given to and from neutral players(9-12), and possibly even extended players.

To be absolutely sure, this would be a good case to follow the "make a test map" rule and actually make a test map. I would do it myself but I'm going to sleep in a few minutes and it's your question, but all you have to do is make a map, place 2 start locations, set a player to human, and set his upgrades for like, terran ground weapons to 4 (naturally place a marine for the human player too), then 10 seconds into the game give his units to another player, and voila, you have yourself a completely fool-proof, 100% answer which wouldnt even require a topic in UMS Assistance, in probably less time than it took your browser to load SEN and make the post asking for the answer which you could have gotten yourself.

Player 12 does not take or give tech ups, only 1-11 (maybe others, but not 12). If you have a p12 zergling with speed researched by default, and give it to player 8, player 8 will not gain the speed research.

weapon/armor ups never transfer (although they might if you set the max level for the upgrade to 1... highly unlikely though)

You sure about that?

No, they won't.

I am sure.