yes, just go to the current project page and "release" all your add-ons and then you are able to re-assign them to the new project.

Your themes and add-ons are safe & will always be available to you. You will simply need to release them from the old project and re-assign them to your new project.

You will need to do this on your concrete5.org account. Not on your website.

You can do this by going to concrete5.org -> 'My Account' -> 'Projects' -> Select the 'Old Project' and scroll down to find and release your add-ons from said project.

Now go to concrete5.org -> 'My Account' -> 'Projects' -> Select your 'New project' and scroll down to find and associate your add-ons to said project.