To change to another layout, use (setf pane-layout):
(setf layout 
      (capi:contain 
       (make-instance 'row-layout 
                      :description 
                      (list (make-instance 'title-pane :text "One") 
                            (make-instance 'title-pane :text "Two"))
                      :visible-min-height 100)))
 
(apply-in-pane-process
 layout #'(setf pane-layout)
 (make-instance 'column-layout 
                :description 
                (list (make-instance 'title-pane :text "Three") 
                      (make-instance 'title-pane :text "Four"))) 
 (element-interface layout))
To change the panes within a layout, use (setf layout-description):
(setf layout 
      (capi:contain 
       (make-instance 'row-layout 
                      :description 
                      (list (make-instance 'title-pane :text "One") 
                            (make-instance 'title-pane :text "Two"))
                      :visible-min-height 100)))
 
(apply-in-pane-process
 layout #'(setf layout-description)
 (list (make-instance 'title-pane :text "Three") 
       (make-instance 'title-pane :text "Four")
       (make-instance 'title-pane :text "Five"))
 layout)
Note: A CAPI layout must not reuse panes that are already displayed in another layout.
CAPI User Guide and Reference Manual (Unix version) - 01 Dec 2021 19:32:34