Some Assets can be advanced (e.g. Project Junebug) and some can't (e.g. Snare!). Is it OK to advance any asset cards to make them look like Agenda?
For example, with the ambush assets the Runner would be lured, but the advance token(s) would have no other effects.
No, you cannot fake advance cards that do not specifically say they can be advanced.
Page 14 in the rule book:
Cards other than agendas can only be advanced if their text box allows it.
Related: http://boardgamegeek.com/thread/892149/can-you-advance-snare
The rules say you can advance Agendas, and any other card which says it can be advanced. If a card says you can advance it, you can. For Assets which don't say you can advance them, you cannot.
If a card does say you can advance it, you can advance it even when it is unrezzed, unless it says otherwise. (Normally card effects only apply when they are ressed and active.)
The answers already given are correct and were correct at the time of the question, however there is a change to how this works as of 2014. The card Mushin No Shin puts three counters on the card as it is installed, this card does not need to be advancable to hold advancement counters, it only needs to be advancable to advance it through the normal advance action. Queen's Gambit lets the runner advance an unrezzed corp card, gambling that it is not an agenda or asset that would benefit from these advancements for credits. Priority Construction functions like Mushin but for ice.
