what i mean is, do i actually have to put 90 points into repair to get jury rigging at lvl 14, or can i have 70 and read a skill magazine right before i level up to get the 90. i've never tried it before, just wondering if it would work

you have to put 90 into it.

The game will assume your "naked" without any "aids" and will off you base stats.

Taking the perks "Ninja, Slayer, Unstoppable force, jury rigging, long haul" Really drains your skill points... leaves science, Medicine, speech, and lock pick low for very long time.