Okay, just for the sake of discussion here is the dictionary definition of contract:
contract: an agreement between two or more parties, especially one that is written and enforceable by law.
On this thread I think we are talking about non-government laws, like social customs, physical and metaphysical laws, matrix rules, and so on. Whatever the case, it seems that a contract is an agreement to limit one's own freewill in order to participate in some consensual venture.
If violating a contract brings upon one painful consequences, that is a restriction upon the freedom to do as one pleases without consequence. If it is impossible to violate a contract while still benefitting from it, then that is a restriction upon the freedom to have your cake and eat it too. If agreeing to a contract means agreeing to the possible risks of doing so, then that is a restriction upon the freedom to enter something without ever having to face that risk.
So, willingly binding one's own freewill may be the common factor here. How is that possible? I can think of a couple ways.
First by agreeing to put yourself under the authority of something more powerful than you. It could be the legal system, physical reality and its laws, some metaphysical law of balance or freewill you cannot ignore, some group you agreed to join or derive services from which can make you suffer if you fail to pay up.
Second, by making a choice at a higher level and then having the force of that choice bind you upon incarnation at a lower level.
This means that the only way to void a contract without consequence is to do so at the same or higher level it was made. Voiding a legal contract must be done at the legal level, a level which is not high enough to void a "contract with physicality" which was made at the soul level upon incarnating.
Or another example: a particular manifestation of karmic law, like a repeating painful experience meant to expunge guilt or teach oneself a failed lesson, becomes null and void the moment you rise in awareness beyond the level at which some regretful action was made, basically by understanding and forgiving.
So I would agree with LipstickMystic (dreamosis paraphrasing) that "pre-life contracts we may have made were probably made in a less enlightened mindspace than we're in now." It's not that a contract necessarily cannot be changed or reneged, but that it must be done at the proper level in order to avoid inevitable or enforced consequences.
Like let's say before incarnating, two souls make an agreement to meet and help each other out in life at a certain point in the experiential sequence. This is not just a casual agreement, since if one resists then the other would suffer setbacks, which is a consequence and thus the agreement is actually a contract. But during life, it may be possible for both souls to agree to change plans at a higher level, and thus the contract is voided without consequence because it was done mutually. It was made on the soul level between two entities, and it can be dissolved on the soul level between two entities. Contracts can change and be voided, but not just willy nilly. I think the same might go for births, abortions, miscarriages, and so on.
I think there is a subtle difference between a simple "agreement" (which any party can abandon without consequence) and a "contract" that is properly changed or dissolved. Neither then carry consequence, but the contract is a bit more weightily entered and weightily dissolved.
Acquiring fringe knowledge is like digging for diamonds in a mine field.