All Actions: Is there a template for a letter of commitment?

No, there is no such a template. It is important to give some details on the foreseen activities (including e.g. name of the work package where one will be involved; or the time frame). The information given here should correspond to the information given in part A and B of the proposal. Additionally, it is good style to sign the letter. In case of re-submission do not forget to update the letter of commitment with the new date.