This repo collects a number of miscellaneous asm hacks that have been created for Pokemon Fire Red (V1.0). They've been modified from their original versions in order to support easy installation with armips. Armips is a specialized assembler that is particularly well suited for rom hacking purposes. You can get it here.
Every routine has an accompanying README.md file that will give you more information on what it does, who originally made it, and specialized installation instructions (if applicable).
Generally, the installation will involve opening the feature/main.asm file to touch up some definitions - for example, the offset to put the code at - then you will run /path/to/armips feature/main.asm. Then you're done.
A hex editor is entirely uneccesary - rather than outputting a binary file that must be manually inserted into your ROM, these routines will make a modified copy of your ROM with the routine applied. Each of the routines assume that your source ROM will be firered.gba and your target ROM will be test.gba, though both filenames can be changed when you open main.asm.