There's a way to cancel out of playing through the first mission "Give Me Liberty!"...but the cost may not be worth it (i.e. a mission failure recorded in the stats).
There is a glitch in the way that the game engine allows a movement action (such as a fall or jump) to remain in memory between mission attempts. When the game initially begins and the opening montage has finished, the character is dropped at a specific spot on the bridge - which acts as a triggering mechanism to initiate the cutscene with 8ball. If you listen closely, you can actually hear the character being dropped. If a movement is in memory, the trigger spot is missed and you can free-roam, do side missions, and save the game before any storyline missions have been completed at all. Note that the glitch must be performed BEFORE you enter the destination corona at the hideout...otherwise, successive attempts will begin there instead of on the bridge.
The easiest way to perform the glitch is to destroy the Karuma right after the cutscene...and have such a movement action in memory before the mission failure fadeout completes. Even simpler is to back up the Karuma to the Unique Jump ramp on the bridge. Driving up onto the center divider, stop near the gap and push the car to the street below (this will usually result in the car flipping over as it hits the road below the bridge). Immediately when the failure message appears, fall into the gap yourself. Your protagonist will be picking himself up off the street as the screen fades out...and that action is carried over to the next mission attempt - which causes the trigger spot to be missed. Those who are using the PS2 version will notice that the protagonist appears to be "locked into" moving forward only...but this problem can be corrected just by sprint-jumping or falling. PC users have the advantage of the mouse to point the camera in any direction...so this problem does not appear to affect that version.
As mentioned, the cost for performing the glitch is a mission failure recorded in your stats. AFAIK, there's no way to keep a movement action to remain in memory after using the "new game" option...so failing an attempt appears to be the only way of breaking out of the intro mission AND keep such an action in memory to cause the trigger mechanism to be missed. Getting busted or wasted cancels out any action...so destroying the mission vehicle might be the only way.
The SI and SV safehouses can be used immediately...since their doors are always open when not on a mission. The Portland safehouse is locked, however (because it's intended that 8ball unlock it for you). You can still gain access to this safehouse by forcing yourself through the wall (sprinting against an ambulance parked lengthwise along the wall works well to defeat collsions). Doing that will open the door and you can use it normally afterward. Be aware that using a speedup code is not necessary to force yourself though walls (but it certainly makes it easier). Though preserverance, you can perform this glitch without resorting to codes at all. Just try sprinting into a tight gap. The ambulance's narrow cab is a good target when it's parked along a wall. Park another vehicle on the opposite side to prevent the ambulance from sliding away from the wall as you sprint into it.
Saving the game with no missions completed will not reflect a name for that save slot...it will be blank on the PS2 version, and read as "no data" on the PC version IIRC. Loading the game will still function normally tho. If you complete a side mission that has a specific name assigned to it (i.e. any of the offroad or RC missions), the game save will use that name.
Since the storyline never gave you a change of clothes, you will remain in your prison jumpsuit until you have actually brought 8ball to the hideout as intended.
The Callahan bridge will not have barriers. The wreckage will remain, tho...so performing the Unique Jump on the center divider is not possible (it looks to be impossible to even initiate). Again, these attributes will remain until you have delivered 8ball to the hideout.
Revisiting the triggering spot on (or below) the bridge while on foot will reactivate the cutscene and allow you to pick up the story whenever you want to (so be careful when walking around). Any weapons or cash you obtained will remain...but armor will be lost if you had it. Reactivating the cutscene also has two other side-effects:
The Portland safehouse will be locked again if you unlocked it manually (via forcing yourself though the wall).
The game clock is reset to 4am...without altering the # of days passed stat. This is somewhat useful...since you can complete some side tasks after breaking out of the mission, and then revisit the trigger spot before the clock reads midnight to keep the stat locked at zero days. In this manner, you can complete all side tasks except Paramedic (which takes more than 20 hours to complete to level 12) and the mentioned Callahan bridge UJ (impossible to do until the wreckage is cleared away)...while continually revisiting the trigger spot between tasks (and before midnight) to prevent the days passed stat from rising. The extra mission failures in your stats may not be worth the cost in ones' own opinion for a "starter save"...tho. Make your own call about that.
It goes without saying...but any other side tasks which are impossible to complete immediately AFTER the intro mission are still impossible using the glitch (such as obtaining a BF Injection for the SV garage...or activating any of the telephone employer missions). Such tasks are only possible to complete after a given amount of storyline completion which unlocks them.
Any vehicle you have parked will remain when reactivating the cutscene...but is (always?) erased when performing the glitch to break out of the mission. The intro mission will clear a carryover wanted level you have after a couple moments, tho...so a funny trick is to lure police to the trigger spot and step on it when a bunch of them are surrounding you - then watch them slowly lose interest as the next attempt begins.
BTW you can see some pictures of using this glitch on Noops' pages:http://noops.gtaunderground.com/Free.htm This post has been edited by Nukey Shay on Monday, Mar 26 2012, 09:28