Sounds a bit like wasting a perfectly good voodoo and the PCI ones are approaching something of a holy grail nowadays, don't they?
But if you insist, what Doornkaat writes seems plausible and doable for a layman. Meaning, find out how and change said resistor.
Or, since the power consumption of that chip might actually not be that huge, you might even get away with simply bypassing the main conduct with some kind of external load, if Ohm's law means anything to you.
(Ya know, what Germans know about resistance.)
So, that will not reduce the power consumption of the rig, but of the chip.
Software, frequency: I remember a tool called the riva tuner. Was named for the Nvidia card, but did a lot more.
Anyway, running hot is not a vice per se. They do work, don't they?
Anecdotal, but I admit, I've actually fried my original '3000, maybe 12 years ago.
Remember, that was the time when an obsolete voodoo was just a piece of junk.
(Which is the reasons why today it's a rare piece of junk.)
It got replaced by a Gf4 around '02 and went on to my father's Athlon - that was an evil scheme of my brother and me to groom it as a standby lan party rig.
We had previoulsy fried the cheap biostar slot 1 motherboard by adding a gf256 to it and I installed the voodoo once I realized the VGA signal of that gf256 looked like a potato.
So, it croaked a few years later.
Back then we didn't know any better and didn't care to much about the hardware longevity of daddy's solitair machine.
But looking at that late 90s mini tower case some years later: That thing was a death trap.
Hardly any ventilation, whatsoever. Shouldn't have housed anything beyond socket7, unmodded.
So, if you've heard about dying Voodoo3s, its probably due to extended stupidity of that kind.
IMHO: Leave the slot below it unpopulated and use a serrated bracket or none, you should be fine.