Instead of

 Set %Password $rand(a,z) $+ $rand(a,z) $+ $rand(a,z) $+ $rand(a,z) $+ $rand(1,9) $+ $rand(1,9) $+ $rand(1,9) $+ $rand(1,9)

Why not have

 Set %Password $+($rand(a,z),$rand(a,z),$rand(a,z),$rand(a,z),$rand(1,9),$rand(1,9),$rand(1,9),$rand(1,9))