Tap into motherboard parts?

Looking at some spare mobos, I just noticed that they use common parts ... LM85s and such, typically SOIC packages, monitor 2 temps and control 2 fans, that sort of thing. Parts differ, capabilities are always similar, datasheets are easy to find.

Can leads be piggybacked onto the relevant pins and drawn out to external temp monitors / fan controllers?

Obviously you'd want to be careful to draw as little power as possible, since you don't want to disrupt normal operation of the part. Or maybe you do? Pull power away or inject power into the various sense pins to control (or at least influence) the mobo's internal heat and fan sensors?

Or maybe just desolder the part completely and mount your own programmable version?

Just ideas, looking for feedback or just hoping to inspire. Wondering if it's workable, or worth the effort, though it's not something I plan on doing anytime soon.