When Steam is in offline mode, the games also don't connect to a Steam server so you should be safe. Keyword being "should" because I got a reply from a community mod that said:
I think VAC is turned for Solo play too. Please refrain yourself from using trainer/hack software. You are risking your account.
Once again, use the trainer with caution. Best to use it while in offline mode. I'll update this thread later if I get VAC banned in about a month or two...:/
Could be sooner i allowed a guy to use family share on steam for 2 days while i was out of town on the weekend after COD:AW came out that Monday morning what ever he did while "testing the game before he bought it" caused my 11 year old level 50 steam account to get a vacbann on it.......Wooo talk about almost making a grown man cry.
I already explained how VAC works in the trainer thread, when it comes to the mod's response, he's a dev, you don't expect him to say sure use cheats do you? as I said, I explained how VAC works, you can trust in it or do as you wish.
[Edited by Sapphire, 3/13/2015 2:41:02 AM]