Hi dude,
I must apologise for the delay in replying, even though nothing I could have done would have shortened it  :  )

If you think of brain development as analogous to body development, what most of us have ended up with post-school is the equivalent of one huge muscle-bound arm (N5) one thinner but serviceable arm (N4) and two little skinny weak legs (rear nets). If you imagine this, it suddenly seems very clear what to do.

Obviously most of our exercise plan needs to concentrate on those little legs, build them up so they can better support the body, but that doesn't mean we can allow everything else to waste away in the meantime. That's what hacks are for; to keep any networks busy that may be overdeveloped, with healthy tasks to do instead of wronguse. So stuff like chess is great to keep that big muscley arm happily occupied while we work on the rest.

Hacks are there to protect against wronguse. Any healthy activity can be used to occupy a network, and your input control should be about selecting them so that you can concentrate on building up the weak nets without boredom, distraction or interruption.

Your only enemies are wronguse or nonuse. If you replace something like TV with chess you are doing your brain a great favor, even if N5 is overdeveloped.

Programming, incidentally, is more likely to build up N4 than 5.

Having a job that exercises only one or two networks is not so much a problem unless it's wronguse; (there's a big difference for example between programming and telesales). In such a position we need to spend more of our spare time exercising the others, so we allocate more time to practising exercises for weak networks, keep the 'overactive' guys busy with hacks, and also include some exercises that can get all the networks working together, for example playing a musical instrument.
Best,
AR