OK, so technically this isn't a hack because it's detailed on pages 230-231 of the CSR, but I seldom see it discussed or used so I figured that a highlight might well bring light to an underserved option in the CSR.
So what is an XP Advance?
The XP Advance mechanic is meant to open up an additional level of customization to players during character creation. This allows players to gain pre-game experience they can spend on advancements or on other medium or long term rewards. The cost of this bonus experience are story complications of varying severity. This could take the form of a hated enemy, a bum knee, a skill inability, a dependant NPC, or even a story requirement for future advancement.
The idea here is the ability to tweak characters a little more at character generation. Maybe you want to portray an older character who has more experience and has seen a bit of the world. Taking an some XP advances will allow you to buy one or more Tier 1 Advancements like an extra skill or ability or perhaps some additional pool points. The balance are some complications which can help to further flesh out your character's background and deepen the story behind your veteran PC.
As an example:
Tom is making Quickfingers an Honorable Thief (Explorer with stealth and skill flavors) who Works the Back Alleys for a Cyberpunk game. He wants his character to be somebody with some experience. The veteran of the group who has a little more experience in the shadowy underworld of this near future setting.
Tom works with the GM, telling him that he sees his character as having been burned in the past by an unscrupulous client. The result is that Quickfingers is a wanted man by authorities. Worse still PhiMicroDrone Inc. (Φ) knows that Quickfingers was the one who stole their prototype. The Φ Corporate Security has an active investigation open, and their investigators, as well as hired bounty hunters, are hoping to get their own brand of "off book" justice if they can find Quickfingers before the Angeles Metroplex Police do.
In return for this story complication the GM agrees to advance Tom 16 XP, enough to make Quickfingers a Tier 2 character from the start. The other PCs will only be Tier 1, but initially Quickfingers and his player will have to deal with the AMPD as well as Φ Corporate Security.In this instance Tom is gaining a full tier advance over the other players, but the story complications should be sufficient to balance this out. The GM would be expected to make Quickfingers life difficult as a result of his complication and Quickfingers finding a way to clear his name (or at least redirect the blame onto his client) should be a major portion of the game's early play. There is likely an understanding that the other players at the table may gain more experience early on possibly by way of the GM no granting Tom XP when Quickfingers' story complications lead to a GM Intrusion (though those GMIs should still generate 1 XP to be given to another PC).
Likewise Quickfingers backstory may contribute to NPC reactions and comments. A potential client of the group may not want to deal with the wanted thief and instead insist on discussing the contract with a different character. Potentially they may even find that the bounty on Quickfingers' head is sufficient to make enemies of neutral or even allied NPCs.
Likewise background complications need not be social ones. A character who is paralyzed and needs a wheelchair is as viable as a character who is wanted and hunter by the law. Likewise a player may choose to start the game with a missing arm with the full intent of getting a replacement during play. They could take no XP advance for that and simply receive the replacement arm at the right point in the story, or they could take an appropriate XP advance and later pay back that XP as the cost to gain the replacement limb. This would allow the character to start with a little bit of a leg up in return for the complication and may feel more organic to the story.
Of course lesser complications can be taken for lesser advances. Perhaps just a minor foible in return for the XP to buy a skill ahead of time. The point here is twofold, allowing the player to make the character they want to play, and providing more detail for character back story and for in game role playing. The complication balance always needs to be appropriate to the story and group. Likewise these should be used as the exception, not the norm. If all the players are asking to be tier 2 from the get go, it is probably better to just let them all be tier 2 without complication as they will still all start on the same footing.
Do you use XP Advances? How else do you think you could use trade-offs during character creation to customize your Cypher System character?