What I might suggest is this: upscale the original low res .tex file to double it's pixel size, re-pack it as a.tex with the same palettes/CLUT, and then save over the hi-res file and repack the .fs - if the hires folder has 4 different .tex files for the 'quadrants' you will need to upscale the low res .tex file to double it's pixel size, cut it into quadrants (keeping the palettes and clut in-tact) and then ripping each one to .tex files with the same names and memory amounts and saving over the ones in the 'hires' folder and THEN repacking the .fs -- sounds WAY too arduous just to get different icons... what I think we need is the following:
If we found the assembly pointers to the directxinput codes, you could use Hext tools to redirect the assembly pointers to the ones you've found in Deling. This -might- even be possible using assembly pointers to the low-res icon.tex folder, but might not work since the scale isn't set properly... however, if it's dependent upon a set of UV quadrants, it might work out-of-the-box.
Unfortunately, the only 'for sure' way to get the look you want, you will have to either follow the above technique with packing .fs files or use tonberry (super easy) to direct to the SeeDReborn hashmaps - and instead of using the seedreborn textures, you take the palettes from the icon.tex file, upscale them to 2048x2048 and then cut them into quadrants, renaming them in accordance with the color palette layout of seed reborn. You -could- technically only need to do this for iconfl03_17.png (the rainbow texture) You can do this with your own sysfld file as well, if you find the one from the PSX version (it will give you your original font).
So - tonberry rundown:
1. extract the icon.tex file's 'rainbow' palette and convert it to a 2048x2048 png
2. cut the bottom quadrant out of the 'new' 2048x2048 image and save it as a 1024x1024px named 'iconfl03_17.png'
3. install tonberry enhanced (move 3 dll's and 2 folders into your FINAL FANTASY VIII parent folder)
4. put the seedreborn hashmap into FINAL FANTASY VIII/tonberry/hashmap
5. in FINAL FANTASY VIII/textures, create a folder named 'ic' and then a folder within that named 'iconfl03', and place your 'iconfl03_17.png' texture in the folder.
You might be able to do this with tonberry at 1x resolution, but i don't think so? you could always try to go to FINAL FANTASY VIII/tonberry/prefs.txt and change it to 1x, but 2x might be the lowest you can go. In that case, instead of upscaling the low res .tex palette to 2048, increase it's size to 1024 and then follow the above process using a 512x512 iconfl03_17.png texture. Even if you get it to do 1x, you will have to still upscale your image from 128x128 to 256x256 and then cut it into quadrants and use the bottom right quadrant because of the game referencing the 'hires' folder in the backend.
The 'old' PC version and the old launcher let you use low res fonts, I believe (Launcher 1.31 - ancient news here) so if you could find the assembly pointers between the two versions using Deling, you might be able to accomplish your original task of using the low-res folder and then you don't have to worry about any of this lol