Ok so, after trying almost all of the platform ids, I tried booting with "0x59270004", and also I noticed that "Graphics > Inject Intel" was disabled, and booting in verbose mode said that the "-disablegfxfirmware" entered in conflict with IntelGraphicsFixup.kext. Then I ticked the Inject Intel checkbox, i remove the -disablegfxfirmware flag, and after a reboot I had my custom HiDPI resolution. I really don't know if it's working thanks to this specific ig platform id, or to the other modifications I did to my config.plist, or maybe a combination of the two. Anyway it's working, thanks for your help
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