The front length of the boot does not interact with the ice. (Because the boot doesn't touch the ice, unless you fall. Though the sides of the boot may touch in a lunge, or in extremely deep edges and crossover and progressive underpushes.) Hence, there is no reason why different length boots means you need different length blades.
(Unless, of course, your feet have grown.)
(And of course, the front of the boot does limit how close your other foot can come, so if you like very close "neat" feet, you may have to change the way you skate a little.)
However, you might want to consider moving the blade mount points. Most skate techs mount the front of the blade flush with the front of the outsole, even if the boot is significantly longer than your foot, unless you tell them otherwise.
A plausible place to try mounting the blades would put them in the same relationship to your feet that the last boots and blades had.