You are confusing the baro readings. When you get a baro reading from a weather station, it is corrected to sea level. The density altitude correction is covered by the actual physical altitude.
If you take an absolute pressure reading at altitude, you are getting basically a PRESSURE altitude. If you put 24.92 and 5000 feet, BOTH into JBM, you will be WAY off target (unless you uncheck the little box). One or the other.
Yes, pressure changes over altitude, but that is predictable. And JBM takes that into account when you put in the altitude.
Try it, put in 29.92 as the pressure and then change the altitude from 0 feet to 5000 feet.
For my .308 load, 80F, 80% RH at 0 altitude, come up for 1000 yards is 11.3 mils. At 5000 feet (still with pressure set at 29.92) the come up is 9.9 mils.
Notice in JBM, under the Pressure input box, is a check box that says Pressure Is Corrected. If that is checked, it corrects for altitude, and the minor changes in pressure from weather are INSIGNIFICANT.
Yes, you can uncheck that box and input absolute pressure, but then it does not use the Altitude input.
You can use either, but bottom line is, you do not need a pressure reading. But you DO need to know your actual altitude (GPS or map) and Temperature. If you have a pressure reading, you do not need to know your altitude. Would I put out the money for a Kestral to add a pressure reading to my ballistics input? No. I have a GPS.
Baro pressure changes with weather, that is not predictable, but trivial.
For fun, I used your data. I don't know your rifle, so I used my .308 load. If I put in 80F, 80% RH, 5000 feet and 29.92 (with the box checked for corrected pressure), I get a come up at 1000 yards of 9.9 mils. If I put in 80F, 80%RH, and your pressure reading of 24.92 and UNCHECK the pressure box, I get a come up of 10.0 mils. Or a difference of 0.1 mils or 3.6 inches at 1000 yards.