At present after the creation of a project property, there is no mechanism in place to edit it. If you realise quickly enough that there is an error, you can uncreate the project property using the Undo Command (Ctrl+Z) and re-create it.
If however, you’ve already undertaken several different actions since the property was created or even saved and closed your project (an action which clears your undo journal stack) undo will not be a viable option and you will not be able to delete the project property.
If you create a project property IGI recommends that the first action you do following its creation is to review it and make sure any associated equations work as expected. This is best achieved by quickly creating a new page and placing the project property and any inputs to equations onto it.
Made project properties will only be present in the project you are working in/on and will not persist across new p:IGI+ projects unless you decide to share/transfer the made project property between projects (See Sharing project properties in the p:IGI+ user guide: https://www.igiltd.com/software/igi-software-user-guides/pigiug/createpp/).