Is this a bad idea? Extreme speedometer tuning

I recently replaced my instrument cluster and the mileage is about 50,000 miles too low. I was going to pay to have it corrected but I was looking at the speedometer tuning on hptuners.

I think I could fudge the numbers to make it go like 15,000mph. Lol. There is a warning about bricking the pcm if you set the values too low but not too high. Would this hurt anything? This would save me $ and save me from removing and shipping out my cluster. Seems smart I just wanna make sure I don't hurt anything.

I could let it idle in the driveway in 6th gear. Fuel cuts out at 255 so I'd let the computer think I was going 250 when it's actually going 50. And then I could change the output from 4000 ppm to 250,000. So the cluster would see about 15,000mph. I could let it sit like that for about 3 hours and I should be good. It's like ferris buellers day off but opposite.

Well I tried it. Fastest speedometer will accept is about 200mph. That would take 250 hours so I'll just pay to have it changed.