Slitherine

Playing against the AI i was able to click on a german tank and make it elite, did not cost me any money and i don't know why anyone would want to do this, but it is a bug.

Not sure how it works, but I have read same bug report about renaiming opponent's units.
Personally I can't select hostile units (and make them elite/rename) - just nothing happens when I click on them, so don't know how it works.

It's possible to "select" an enemy unit by scrolling the screen so that the unit has some graphic off-screen, and thereafter moving the cursor on top of the unit and down to the dashboard. Then, the unit will be "selected" in the left dashboard window.

I haven't tried the elite trick, but I figure that's how people manage to do it.

You can only upgrade units to Elite in core home hexes.

Only Germans can purchase elite. When you select the unit the "Elite" button will highlight for you to purchase.

You must have enough positive funds to do this.

Russians by default earn Guard status through combat. You can change that by changing the game setup option when the game is created / started.

It has something to do with a fog of war, sometimes a unit will appear for no reason in germany and you can select it.