Is it the Scaled Max that your are trying to change? If so, then if you are online, you would have to run throught the 3-step process to put your change into action. If you are editing the SCP Output, then when the PLC scans the instruction again, the Output will be recalculated and put back just like it was!
Okay, the Input is being calculated or dervived somewhere else, so it overrides your change on each scan of the PLC. You would have to find where "Input" comes from (looks like N10:111), and "force" that value.
If N10:111 is not being set by some program instruction, but is simply a constant, then go to Data Table N10, select word 111, (Radix - "Decimal"), and type in your new value. Make a note of what N10:111 was before, so you can put it back when you are done testing.