Bud grafting/chip budding can be very useful
It's commonly used in Japan for for entirely swapping the cultivar of mature Ume bonsai (for changing the flower type, foliage type, or other characteristics and habits), and this works well because it can be more discrete than using scions. I personally find bud grafts easier to use when working on smaller material, or in tight spots.
The success rate can be quite high. I did two all the way back onto the trunk of an old Ume (to start a new primary branch in a new location), no problem.