The last option you gave is the correct one.
Let's say you have 68% on spin and buy this rod. Then 68+7=75% that means when using this rod (and this rod only!) you should be able to use new abilities in the tree, like wacky rig (70%) as well as Texas (75%). However, it does not make it possible to put points in those abilities, so you gotta use it without any points till you actually unlock it. It's great for testing new abilities, but it doesn't make it easier to catch trophies nor regular fish.