The SPMod is not a total convertion or a "complete" mod, it's just a new game dll meant to provide more tools for mappers with little knowledge of C while maintaining compatibility with the original game. A few gameplay tricks have been added, but you can disable them using cvars.
Fixes
- The shopkeeper does no longer say "sorry, I ain't any" when selecting blank items
- Removed prices for inexisting items in Pawn-o-matics
- Redrawn slot5.pcx to avoid the blury bilinear filtering
- Captions pointing to wrong actor (some answers were credited to player instead of sidekicks)
- Player could trigger the reload animation for most weapons even though no spare ammo were available
- Instant death, freezing cast_bum_sit fixed
- cast_whore and cast_shorty now properly equip the flamethrower
- Fixed a terrible bug introduced by the SPMod (unable to reload the silencer)
Mapping features
- cast_bitch, cast_thug, cast_runt: added spawnflag 1 (Lockpicking skills for friendly one-handed weapon characters)
- Friendly characters can now be named whatever you want
- Friendly characters asking from 1 to 9 bucks will now be instantly hired for free
- Pickup items: added spawnflag 128 (trigger_pickup, they can fit almost anywhere and can only be picked up when triggered)
- trigger_once and trigger_multiple: added spawnflag 16 (can be toggled on and off)
- trigger_relay: added key "random" (chances, (from 0 to 100) for the trigger to fail and not fire its targets)
- func_explosive: added spawnflag 16 (autosound) and 32 (damages must be inflicted at once, or the brush doesn't break)
- func_button: added spawnflag 8 (don't move) and 16 (remove itself when triggered)
- cast_bum_sit: added spawnflag 1 (drunk)
- Custom pawn-o-matic stocks
- More scriptnames for path_corner_cast
- Accuracy mod for pistol (available in Pawn-o-matics and pickup items)
- Slowburn mod for flame thrower (available in Pawn-o-matics and pickup items)
- Custom log entries and episode flag registering in SSF files (target_register_epflag)
- Support for custom models (misc_model)
- Advanced keys (items or episode flags)
- Level designers can save the player's game when approaching tricky sections (target_savegame)
- func_spray: creates a gaz of pipe or something similar, barrels 'o fun.
Gameplay features
- The Special Order key can now order any gang member to hold a distant position (aim at the position and press the Action key, cannot be used in a KP episode)
- More cheat codes (see console command "sonofsam", "itemlist" and "epflag")
- Several damages tweaks (see console command "cl_noratbite" and "cl_healthregain")
- Customizable gang size (see console command "g_maxgangmembers") 

https://kingpin.info/hosted/kingpinentityguide/