Do you mean you want customized tags? There is already a field for track number, but “Singer” is not standard for [u]ID3 Tags[/u]. There is “Lead performer(s)/Soloist(s)” ID3 tag, so maybe you can use that.
I rarely use Audacity for tagging, so I can’t really help you with it. [u]MP3tag[/u] is a handy tagging application that can do almost anything that’s legal in any tag format, and it works an almost all file types, not just MP3.
What file format are you using? There are different tagging standards for different formats. MP3s ID3 tags, and there are a few different versions of ID3. There is a “Comment” field that you can use for almost anything. Or, you may be able to hijack another field if you don’t mind having the wrong title for the field.
Ogg Vorbis/FLAC tags allow you to create any type of tag you want.
The next issue is making use of a custom/special/unusual tag. If you have a non-standard or uncommon tag, your player/library software may ignore it.
You can’t remove the seven default Audacity tag fields but if you leave their value empty, Audacity won’t create those tags.
You can add your own default fields underneath the seven Audacity fields, by pressing “Add” then “Set Default” then OK. Then every time you open Metadata Editor, you will see your extra fields.
But note there is an Audacity bug that the custom fields you add won’t appear next time you open Metadata Editor if the values are empty. So click in the “Value” for each field you add, then click SPACE on your keyboard to make a space in each value, and your custom fields will always appear.
If you are exporting MP3 files, every custom field you add will have the “TXXX” “user-defined” frame, even if you give it a standard name like “Album artist” or “BPM”. This is an Audacity limitation, but unless your player can read TXXX tags, it won’t see your custom tags. Even if it can read TXXX, your tag won’t appear under the standard name.