PS-X EXE Modding

[Z3R0X]

Hello everyone, I'm new around here, also kinda new to PSX game hacking, I do simple mods on games that act like cheats, fixes or game enhancers, sometimes I came across a routine that do something that I want to change, but I don't have enough space to inject custom code so I need to insert a JAL, do my stuff, return and continue normally. So I need to store my custom code on the SLUS in order to jump there.
What I do is injecting code in the leftover strings from the SDK (CdlReadS, CdlSeekP, CdlSeekL, etc.) these strings for some reason are on RAM all the time, but is only around 300 bytes of space and sometimes I need a lot more.
My question is....
Is there is a way to inject more code (at least a sector worth of code) into RAM from the SLUS?
Some people tell me to look for unused system fonts, but some games do not have fonts leftovers into SLUS.

Thank you for your attention.