Yes, that is right in theory. However, your bow may never have shot 70 at 29" if it goes up to 30 or 31 inches. Also, if it has stretched that much your draw length would be longer as well. Is it?

You can do what you want, but I don't think that I would dare twist an older cable enough to add 7lbs of draw wt to it. Could be asking for it to blow.

Also you must add twists to the string side as well.

Twisting the cable will change the draw force curve of the bow by adding preload to the system. You will have to set the tiller and timing and generally retune it when you are done. Nothing will be as it was, your nockset will be off, peep, kisser, everything.

It will be less drastic a change if it is a small idler single cam system, which I think it is.

Best practice. Go get new string/cable put on it.

Hope this helps,

Dryridge