Yes, of course you have done something wrong. LFS is a licenced product, in so much that you have to purcahse the sim to make use of the cars and tracks not unlocked in demo mode. Circumventing that process is to all intents and purporses theft.
Is stealing a TV from a shop so you can try out the features, regardless of whether it makes you want to buy it more, a right thing to do? Surely that is also theft, and punishable by law. Would you even consider it? Probably not, but why crack LFS if it's technically the same thing.
Oh, and you CAN use tweaks online, so long as the server and all participants use exactly the same tweak (iirc).