There is no limits to open a container if its been opened by an script (as long as i know and tryied).
You can do this too but i still don't think this is the best idea... i already had thousends of problems cuz of strange behaviors of sphere... i keep thinkg if this item transfer happens when sphere starts to save the world, if there is an resync or anything that could mess with the server processing could be a hudge problem.
I've allready sayed my opinion: share the entire bank, create an systen to players improve theirs banks to store more itens and this kind of stuff
If is there something more i could help, feel free to ask!
See yah!
Other thing you can do is this:
1) Creates a dialog that shows all the charactes
2) When the character is choosen, change the layer 29 (bank box) type to t_container, change the attr to invis and move the box to the player bank (inside the bank)
3) Open the box and create a event to "restore" the bank after the player logout (this is the best way to restore the bank back, its a little hard to trigger when the container is closed, this way the bank will always back to the right character)
NOTE: You have to create some verifications to see if the box you want to open isn't already inside the bank of the player... if you won't do this there is a chance that some players "lost" theys boxes