in this case you should drive the simulatin with a bash script: Example:

# Delete output file, ngspice should have 'set appendwrite' so multiple runs will append data

rm outputfile.raw

#run simulation

ngspice .....

#change corner in circuit netlist

sed -i '/^\.lib/s/tt/ss/' circuit.spice

# run simulation

ngspice ...

You shoud create a loop if needed