For the sake of argument, lets sidestep that we can't effectively induce earthquakes in a controlled sense (i.e., we can't do something that we know for sure that will generate an earthquake of a target magnitude) or that wholesale changing the style of strain release of a given fault zone from something like 1 Mw 8.0 every 100 years to 1 Mw 5.0 every day (which is effectively what you would need to release the same radiated energy of a Mw 8.0 in Mw 5.0 events spread out over 100 years) is impossible.

Let's instead entertain the idea that there is some mechanism to start this process, i.e., we begin chipping away at the stored elastic strain sufficient to generate a Mw 8.0 with a carefully targeted Mw 5.0 event that we some how arrest the rupture of to keep it at a Mw 5.0. What did we accomplish? Well, we released a miniscule fraction of the total radiated energy we need, but we also have now changed the stress state on other parts of the target fault and neighboring faults (and in this, we need to remember that virtually no large fault is a single fault, but a network of faults, i.e., a fault system) through Coulomb stress transfer. So when we move to our next "patch" to try to rupture, the stored strain (and proximity to failure, etc.) will no longer be the same, not to mention we've now loaded adjoining faults, etc. The point being, you can't just have patches of fault fail in a vacuum, each one will impact the state of the system and not always in the direction you want, i.e., an earthquake on one patch can increase the strain on another patch, etc.