[GRASS-user] some questions (fc Update, Clip and attribute table)

Hi all,
I am new here and to grass, so I have some questions about working with grass.

First,
I have some maps and one line, witch represents the boundary of area. And I need to trim my maps with this line (somethings like Clip by ESRI). Is it possible with Grass tools?

Next…
To my polygon map I want to add some polygons from other polygon map (Update, again like ESRI). I am not sure if v.patch is the best solution to get this

Next…
Can I edit the column header (name and type) of attribute table? I know another WIN software that can it do, but i am interested in GRASS now. Is it possible to remove some columns from the table with Grass?

I would be happy if you could me give any answers.
Best regards
Martin