the easy way (if the starting color is tan or light brown) is adding dark brown wax (not paste polish) at the areas you want or see at the photo! then buff with a brush! if the result is what you want stick to it else add some more wax and buff again !! with this way the transaction from color to color ll be smoother and it ll give more depth at the color!
this is the best way to go but if you havent a basic experience of using an airbrush it ll probably end like a mess ! (airbrush (especially the gravity feeded) tend to spit the color that trapped at the tip of the needle of the airbrush , a suction feeded one for this cause would be a better choice ))
Stripping them and using leather dye is the proper way to do it, but it depends on the finish already on them and your patience with the process and risk tolerance (possibly screwing up your shoes). In general shoe polished will change the color of your shoes, but it happens slowly over time. If you try to just glob a bunch of polish on at once they will be resistant to shine and an utter mess.
summery of both ways! i have made a post with a pair i changed color and antiqued in the shoe damage thread! always happy to help!