Marshalling will be consistent and the marshals will be trained, they are there to make sure the competition is safe, fair and fun.
Don't worry about the written warning thing too much, it's an alternative to the way points were docked in Lithuania - the marshals won't have the power to do that in Portugal (unless you shoot the wrong target for example). They'll just give a written warning instead, but it won't be done in an unfair way.
If you've just made a genuine mistake or it's pretty trivial, more often than not the marshal will just let you know with a polite chat, no need for a written warning.
If you're breaking a rule that could end up giving you an advantage over other shooters (cheating basically!), then you'll probably get a written warning for it and that might result in the loss of a target - the amount of evidence available and how many times you get warned for the same thing by different marshals might have a bearing on how that goes when it goes to a jury too.
It'll be done in a consistent and fair way. I'm running the training course for the marshals, and I'll be on the jury - but I probably won't be involved in any decisions for UK shooters - it wouldn't be fair if I did that, because there's a conflict of interest.
There really isn't any reason to be too concerned - the kneeling lanes are the ones to be aware of and if you're not sure about the rules, or even if you are and you want to double check - just ask me at Anston and I'll run through the things you need to watch out for.
Do what you normally do at every shoot you go to - but just double check the kneeling rules because they're a bit different to the BFTA rules, and marshals will be looking out for people breaking the rules with their kneelers.