Can people change their karmic experience of difficulty in their life, say they have developed a cancer, by offering to their higher self and Creator to pay this karmic obligation through becoming a Lightworker Healing Protocol practitioner?

People can always do as they wish. We never limit or interfere with human choice. As you know, humans are in charge of their experience. All that they do is honored and allowed. That is not to say all is productive and helpful they choose, only that we will not override human choice. This bargaining can, therefore, be done if it brings comfort for the individual. The extent to which a particular choice of offerings to atone for some known or uncertain past obligations of a karmic nature cannot be decided unilaterally. It is up to the Law of Karma to say when a person has done enough to rebalance something and restore order through their own efforts to make up for a discord done to them or created at their own hands. So this is an exercise that will be ineffective unless there is a divine intervention to assist with the arrangement. So when a bargain is made with Creator, we can see to the implementation in a way that will be effective if all the parties and forces involved are satisfied. So, as with prayer in general, the higher self must agree and there must be a way to balance the karmic energies that is sensible, and if this is appropriate, the divine realm can implement a series of maneuvers to bring about the consequences desired.