I am going to comment this here too science here is also relevant:
I made a web application in html5+js+scss that allows you to customize the percentage of the
Reduced EXP Yield mod(basically allows you to make a file that gives the % of xp that you want 12%, 240%, 99%, 0%, whatever), this application works by you uploading 2 different personal_total.bin files, which can be the ones provided in this mods(the 60%, 35% or 200% ones), or the original personal_total.bin extracted from the game, or the one in the enhanced eevee/polished pikachu(the 75% one), it does not matter which, just 2 different personal_total.bin whit different percentages.
This tool been tested ingame and it appears to work alright, but i'm not 100% sure is not going to cause problems with some pokemon xp because to change the percentage this tool do this:
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1-Put the hex strings in 2 arrays(one for each file), each value of the arrays contain from 0 to 255, or the same from 00 to FF, and create a empty array, array3.
2-Transform all the data in the arrays from hex(00-FF) to decimal(0-255)
3-Create the variable i and set it to 0
4-Compare if the decimal data in of array1
and array2 is equal
4.true-if is equal i convert the data of array1 from decimal to hexadecimal and save the result to a array3
4.false-if is not equal i execute this formula "Math.floor((array1 / original percentage) * new percentage)", if the result is greater than 255 i set it to 255, then convert the result to hexadecimal and save it to array3
5-I add +1 to variable "i"
6-if variable "i" is not equal to array1.length
6.true-if variable "i" is not equal then return to step 4
6.false-if variable "i" is equal, then convert array3 to a hex string and put the string in the third text box
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So if some pokemon xp is using more than FF(255) of data to store its value then that pokemon xp would be set wrong whit this tool, but for the moment it does not appear to be a problem, and even if it happens it would be just 1 pokemon that has not the xp correctly set to the percentage you wanted, but it would not be that far off, for example if it was A1F(2591) and you set the percentage to 50% this tool would convert that value to 515(1301) that is not far off the 50% of A1F(2591) that would be 50F(1295)(I put between "()" the numbers in decimal).
I STRONGLY SUGGEST TO READ THE GITHUB PAGE FIRST AS I PUT CLEAR INSTRUCTIONS ON HOW TO USE THE TOOL ON IT, STEP BY STEP, THE LINK TO THE TOOL IS INSIDE THE GITHUB PAGE
Github: https://github.com/takashi1kun/hex-poke-xp-edit/tree/master
Yes, this is a tool for modding a mod, is metamodding.