Pairs well with light overhaul.

Method:
Uses a simple data-final-fixes script to look up all ammo of the "bullet" type and adds a chance to launch an extra non-damaging tracer projectile.

Notes:
Should be compatible with just about everything.
Shows a X% chance line in relevant ammo tooltips, this has no gameplay effect, it just refers to the chance to launch a tracer projectile. I haven't found a way to remove that tooltip line.