1.) Just add it to the existing list of vlans on the trunk.

Trunk port in question is 3/2. Its using dyanmic desirable trunk negotiation in this case. It's also using dot1q trunk encapsulation.

The clear trunk command excludes unwanted vlans (pruning).

clear trunk 3/2 2-11,13-57,59-150,153-499,511,519,522-579,581-589,593-594,603-609,611-697,700-769,771-1005,1025-4094

set trunk adds vlans to a trunk

set trunk 3/2 desirable dot1q 1,12,58,151-152,500-510,512-518,520-521,580,590-592,595-602,610,698-699,770,1006-1024

So now add vlan 581...

set trunk 3/2 desirable dot1q 1,12,58,151-152,500-510,512-518,520-521,580-581,590-592,595-602,610,698-699,770,1006-1024

clear trunk 3/2 2-11,13-57,59-150,153-499,511,519,522-579,582-589,593-594,603-609,611-697,700-769,771-1005,1025-4094

2.) Not sure I know what you're asking....elaborate?

Anyway, here's the complete comnfiguration guide. Knock yourself out. :-)

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/catos/7.x/command/reference/cmd_ref.html