The cat rescue bods often do this with feral cats. They capture them from an undesirable location, neuter and treat them with long term worming and flea treatment, and then release them at a location like stables, where they can live happily, are fed, and will keep the inevitable vermin under control. Slightly bizarrely a well fed mouser is far better than a hungry one, a strong appetite doesn't make them better!
I presume they have to go back once a year or so, trap them, and do an annual checkup and retreatment.