Yes, if you have collected information related to other MIxS parameters that are not mentioned on our template you can include them so they will be available in your ENA record.
Please also have a look here to get to know other optional parameters for each MIxS environmental package.
If your data is part of or funded by a third-party project, it is recommended to include some background information on the project (e.g. name, acronym, funding agency, grant number) as part of MIxS. This information also complies as a great name for your ‘project name’ parameter.