Hey A1bert ; ) --or anyone else that knows the answer...

Pretty sure it's 'no', but in case I'm wrong: Can I put Cross Training on eWing Guards I added through Temporary Alliance?

Nope as its a skirmish upgrade and not a deployment card.

TryerImp: you're answering a different question. (The question was not about including a Skirmish Upgrade using Temporary Alliance.)

IndyPendant: I think this was answer quite recently.

Edit: yes. This is the (duplicate) thread.

https://community.fantasyflightgames.com/topic/226319-skirmish-upgrades-and-temporary-alliance/