Ok so in the Data Editor under Units tab, I'm unable to remove a unit even though I right click on it and click Remove Unit, same for Upgrades and Abilities
None.

>be faceless void >mfw I have no face
As far as I know you can't remove units from non-mapdepedencies. Basicaly if you copy a unit or make a new one you can delete it, but if it's a default unit you can't. Happily having units from the campaign or multiplayer dependencies doesn't add to file size.
Red classic.
"In short, their absurdities are so extreme that it is painful even to quote them."
So I have to copy all the units and all into a new mod?
None.

>be faceless void >mfw I have no face
No. What exactly are you trying to do? Like, why do you want to delete units?
Red classic.
"In short, their absurdities are so extreme that it is painful even to quote them."
You should never need to delete units.
Currently Working On:
Myself