I'm using tree_sortkeys as a normal sort key as well, and have written the following function to swap two positions. It swaps the two nodes, as well as any children. I'm not a plpgsql expert (only a couple months experience with it), so YMMV, but here it is:
create function brk_class_dev_nodes__swap(integer, integer)
returns integer as '
declare
p_node_id_1 alias for $1;
p_node_id_2 alias for $2;
v_sortkey_1 varbit;
v_sortkey_2 varbit;
begin
select tree_sortkey into v_sortkey_1
from brk_class_dev_nodes
where node_id = p_node_id_1;
select tree_sortkey into v_sortkey_2
from brk_class_dev_nodes
where node_id = p_node_id_2;
if length(v_sortkey_1) != length(v_sortkey_2) then
raise exception ''cannot reorder nodes at different tree levels'';
end if;
-- swap the initial part of any sortkeys that match the
-- above (hence are the nodes themselves or child nodes
update brk_class_dev_nodes
set tree_sortkey =
case when substring(tree_sortkey from 1 for length(v_sortkey_2)) = v_sortkey_2
then v_sortkey_1 || substring(tree_sortkey from length(v_sortkey_1) + 1 for length(tree_sortkey))
when substring(tree_sortkey from 1 for length(v_sortkey_1)) = v_sortkey_1
then v_sortkey_2 || substring(tree_sortkey from length(v_sortkey_2) + 1 for length(tree_sortkey))
else tree_sortkey
end;
return 0;
end;' language 'plpgsql';
