Hi there,
I don't know the exact law in Guatemala nor Mexico. If you speak spanish it will be possible to do some wild camping. To sort out were you can do this it is safer and easier if you are more than comfy with the language.
There are several designated 'wild' camping spots to string your hammock (check LP [Lonely Planet] type of guides).
Bring your own compass and good maps and be prepared for garbage (unfortunately).
A local guide not only knows the way, they see and spot things we wouldn't as easily. Barba amarillo (Yellow beard aka Fer de Lance..higly poisonous viper (or snake ;-)) is just an example.
Depening on the area of Mexico and Guate (mala) I personally would NOT go out without a local guide. Robbery (you rich tourist you) is not unheard of.
I remember vividly one bus ride I took (me being the only gringo) from Huehuetenango to Coban which was held up on the way in, bulletholes in buswindows etc. Having only one way we all feared they would go for our bus too (they didn't).
I spend some time sloggin thru jungles and camping relatively wild, far away areas (Indiana Jones stuff).
Not completely a bushcraft link but I have some (english) travel reports and pic's on my website. Don't know if I am allowed to post that address here since it is not BC related (some pics are tho) ;-), just let me know or pm me.
I had NO problems on ANY airport WORDLWIDE with my parang while travelling between may 2003 and november 2005 (SE Asia, Australia, Europe, The Emirates, Central America). Not as handluggage obviously!
While travelling I sometimes had it on my belt (bushwacking) or it was just in my backpack or in the sidepockets. Had some great reactions while comparing the central american 'wobbly' machete with a Malay parang. Machetes are plentiful in local markets or garden shops!
Pff s-orry for the spelling, syntaxes etc. The day has been too long. If I don't make any sense here, tell me and I will try to clearify tomorrow ;-)
Grtz Johan