I'd say practically none, we were quite memory starved most of the time and even regular scripting engines were a hard sell at times (perhaps more so due to GC

I'd say practically none, we were quite memory starved most of the time and even regular scripting engines were a hard sell at times (perhaps more so due to GC rather than interpretation performance). Games on PS2 were C or C++ with some VU code (asm or some specialized hll) for most parts, often Lua(due to low memory usage) or similar scripting added for minor parts with bindings to native C/C++ functions. "Normal" self-modifying code went out of favour a few years earlier in the early-mid 90s, and was perhaps more useful on CPU's like the 6502s or X86's that had few registers so adjusting constants directly into inner-loops was useful (The PS2 MIPS cpu has plenty of registers, so no need for that). However by the mid/late 90s CPU's like the PPro already added penalties for self-modifying code so it was already frowned on, also PS2 era games already often ran with PC-versions side-by-side so you didn't want more than needed platform dependencies. Most PS2 performance tuning we did was around resources/memory, VU and helped by DMA-chains. Self modifying code might've been used for copy-protection but that's another issue.