Type in the following codes while playing for the desired effect:
|MOREPOLICEPLEASE||Higher Wanted Level|
|NOPOLICEPLEASE||Lower Wanted Level|
|GIVEUSATANK||Get the Rhino Tank|
|BANGBANGBANG||Destroy All Cars|
|NOBODYLIKESME||All People Hate You|
|WEAPONSFORALL||People Fight Each Other|
|TIMEFLIESWHENYOU||Speed Up Time|
|CORNERSLIKEMAD||Improved Car Handling|
|MADWEATHER||Speeds Up Time|
Make Gang members stop hate you:
If you want the gang members to stop shooting at you you can do like this: Open up the pedstats.dat file located in the "data" folder (from the main GTA3 game folder) using Notepad. There you will find columns with the stats for all the different pedestrians in the game. Find the lines named STAT_GANG1 to STAT_GANG7 and change the number in the D column to 100. This is their Fear stats. Then change the number in the E column to 0. This is their Temper stats. Save the file. Now none of the gang members will attack you in the streets.
NOTE: Always make a backup before overwriting game files.