Some years ago I took over a registered company from a friend who was not using it. Through this company I was able to save a substantial amount of tax and so I told my friend I would be giving him a portion of this in appreciation. He did not want to accept it, but I insisted. He then asked me for a post dated cheque as I was not in a position to immediately pay over the amount. When the cheque was due my business had taken a turn for the worse and so I asked my friend not to deposit the cheque. Since then I have not been doing well so I have not considered paying him. Since that I never did owe the money, only by my own insistence, can I now just cancel my commitment?
If the commitment was verbal alone, it can be cancelled.
However, having handed over a cheque, many authorities consider this to be the creation of an indebtedness, the cheque being the equivalent of a shtar chov (a promissory note). Please see here (under the section dealing with cheques) for more details.
Although there may be minority opinions to rely on in retracting, this is quite strained, and the person in holding of the cheque will be able to claim that he is “in holding” of the debt.
Therefore, without the agreement of the other party, it is not recommended in this case to cancel the commitment, and according to the great majority of opinions doing so will not be a halachically valid option.