Most of the time unwanted mutations can be negated by introducing new strains into the mix. If you fear a recessive gene showing itself, throw some more genetics into the mix(something with some dominant genes).
If you want to continue inbreeding then just select ‘normal’ phenos and cull all of the mutants when they show up. It’s no different than someone crossing a pure indica to a pure sativa and trying to select phenos which an indica nature and sativa high. You will have lots of sativa-leaning doms which will need to be culled in order to move forward with what you want.
That’s the joy of breeding imo.