Yup! As a general rule of thumb, I absolutely disband levy ashigaru if I don't need them within 3 turns. Regular ashigaru are more useful to retain if they have several experience chevrons, but if they're "fresh" I tend to disband them as well. I like your recruiting system because it forces me to think about six months to a year in advance.
You might want to ask Akaie from the Sekigahara mod how he did it, or examine their faction packs. They have several examples of individual "bonus faction" packs which replace the Hattori and Ikko-Ikki with another clan.
My (uneducated) guess is that you may have to effectively "reposition" the Hattori to Sakai lands, and then "reposition" the Sakai into Hattori lands.