Gabriel, keep in mind that I only quote policy and have the written directive in front of me. I know from personal experience that on international flights we do strictly adhere to policy and once passenger boarding commences our door is closed except for crew/maintenance related activity. The main reason for the pre-flight restriction is the attention to detail and process required prior to departure.
Bottom line though is that it's the crew members decision...though I would add that in our current furlough/anti management environment (especially domestic) that they risk being turned in by someone with nothing better to do. Dont get me wrong, I'm definitely not against any look/see situation but I'd rather not get written up for something so trivial (I have enough write up's already over the years thank you) so as has been said earlier...you can always ask but be understanding that its not personal if the answer is sorry.. not at this time.
Regards
MS