you seem most worried about other peoples earnings. I bet the fact "mere" guards get paid "a fortune" for pressing the odd button really grinds your gears
If you want to change the T&C's of people you have to do a deal. That means you have to make it worth their while agreeing to the change or you will simply foster real resentment and real industrial action. Perhaps you are able to simply instruct the plebs in your industry to accept your generous and exciting opportunity to do more work in return for less pay. Despite what many posters here desire the railway doesn't work like that.
Your suggestion of part time employees might not go down well with the sainted TOC. Do you you think they want to spend a fortune on training people (and them maintaining competency) to return less than fully productive staff? I doubt it.
Finally I notice you are still ducking the point about cost. How much extra are you prepared to pay on your ticket to fund the 7 day roster? I suspect you wont get it in for the same price as your staff costs now.