Note that while you are free to fork and modify any of our projects at any time, for a pull request to be merged (accepted) you will need to have met our contribution requirements; notably you will be required to have a CLA on file with us. The Foundation uses a GitHub bot to automatically validate CLAs each time a pull request is submitted to a Foundation-hosted project, so don't be shy about submitting a pull request even if you don't have a CLA yet, as doing so will initiate the process. See Contribution Compliance Requirements for more detail.
Some Projects may have additional contributing guidelines; for example requiring a particular coding standard. These will usually be documented using GitHub's Contributing Guidelines feature, meaning that you will see a link to the guidelines from various places in the GitHub UI. Before contributing to a project you should ensure you've familiarized yourself with the project's contributing guidelines, as doing so will help minimize the number of spurious review and edit cycles the PR needs to go through. As a Project Lead you can leverage the template Project Blueprint provided by FINOS to jumpstart your project with proper contribution guidelines.