-- Load all existing metatool assignments for the Expression Tool
local mas = finale.FCMetatoolAssignments()
mas:LoadAllForMode(finale.MTOOLMODE_EXPRESSION)
-- Find the current expression metatools for keyboard keys '1' and '2'
metatool1 = mas:FindKeystroke(string.byte("1"))
metatool2 = mas:FindKeystroke(string.byte("2"))
-- Swap the keyboard mapping for these 2 objects
if (metatool1 ~= nil) then
    metatool1:SaveAsKeystroke(string.byte("2"))
end
if (metatool2 ~= nil) then
    metatool2:SaveAsKeystroke(string.byte("1"))
end