Sycorax
Smash Ace
You can use spot dodge after a DSDI tech to prevent yourself from falling off the stage. It keeps you on stage longer giving more time for friction to slow you down. Here is what it looks like.
Notice that Falco's velocity at the end of the tech roll was 2.82 and after the spot dodge was 1.06, about a 62% reduction in speed. The speed reduction will be different for each character, but this does work with every character.
To do this, hold shield during the tech. At the end of the tech, press down with the control stick. This will buffer a spot dodge for 4 frames. You cannot use the cstick because that requires you to shield for 1 frame which will cause you to slide off. You cannot do a roll with the control stick or with the cstick either because all rolls require you to shield for 1 frame which will cause you to slide off.
This is not a better option than fastfalling to grab ledge after the tech roll. If you are going too fast for that to work, however, spot dodge may be a reasonable option. In most situations, this won't matter because your opponent will still be able to hit you before you end your roll, but it may save you in that one rare instance.
To do this, hold shield during the tech. At the end of the tech, press down with the control stick. This will buffer a spot dodge for 4 frames. You cannot use the cstick because that requires you to shield for 1 frame which will cause you to slide off. You cannot do a roll with the control stick or with the cstick either because all rolls require you to shield for 1 frame which will cause you to slide off.
This is not a better option than fastfalling to grab ledge after the tech roll. If you are going too fast for that to work, however, spot dodge may be a reasonable option. In most situations, this won't matter because your opponent will still be able to hit you before you end your roll, but it may save you in that one rare instance.