edit gtktreestore/gtkliststore structure at runtime

[Andrea Zagli <azagli libero it>]

is there a way to edit a gtktreestore/gtkliststore at runtime after it  
was loaded from a gtkbuilder xml file (made with glade)?

in particular i want to append/insert/remove columns

i could create these columns initially and after show/hide their, but  
i have a variable number of these columns

otherwise i'll create the entire gtk*store at runtime

thanks in advance