You can make recipient lists containing parties you will be regularly sending documents to sign. Such lists are made in the company settings, requiring admin rights. For example, board members can be included on a recipient list for easy signing of minutes.
When making an invitation, pick a list from the load recipient group drop-down menu and the signers will be added to the signer table. You can modify, add and remove signers. Any changes you made while preparing the invitation will not affect the recipient list; it is always modified through the settings.