I haven’t tried this, but I think you could add a 6th entry to your state vector (u0=[990, 10, 0, 0, 0,0]) and set it to a different value for each transition function.
for example
function ctmc_jumps_S_to_L_by_I(u)
u[1] -= 1 # S decreases
u[2] += 1 # L increases
u[6] = 1
end
function ctmc_jumps_S_to_L_by_A(u)
u[1] -= 1 # S decreases
u[2] += 1 # L increases
u[6] = 2
end
Not as nice as something built-in, but worth a try.