P-Slice can store additional information about a given song in a special file called "metadata.json" (mods/your-mod/data/song-name/metadata.json). They're mostly responsible for changing the way this song appears in the freeplay.

Head over to chart editor and click on the "Metadata" tab. It should look like this:

Here are the fields as described above (except song length as this one is set automatically).

Rating (songRating)

• Stores the rating (in stars) for this song. Maximum value is 99, but star bar will only display up to 15.

Show "new" tag (allowNewTag)

• Allows for your song to display "new" tag on the song's freeplay cardcard
• It gets cleared once the player completes it on any difficulty

Freeplay preview start sec (freeplayPrevStart)

• The second on which freeplay's song preview should start.
• Because of the implementation, it'll likely start a bit later.

Freeplay preview end sec (freeplayPrevEnd)

• The second on which freeplay's song preview should end/loop.
• Because of the implementation, it'll likely end/loop a bit earlier.

Internally handled (freeplaySongLength)

• The song's length in seconds.
• This field is used to properly load a song's preview.

Player character(freeplayCharacter)

• The character, to which this song belongs.
• If empty, this song won't belong to any character and any character with showUnownedChars set to "true" will display it.

Song album (albumId)

• The album, to which this song belongs.
• If empty, the album image as well as star rating bar won't display for it.

Song alt vocals (altInstrumentalSongs)

• A list of songs containing alternative vocals for the current song.
• It can be then selected from Inst menu after selecting it in freeplay.

Has erect variant (allowErectVariants)

• Treats "Erect" and "Nightmare" difficulties of this song as a separate variant (located in the '<song name>-erect' song).
• This difficulties will be removed from the erect variant of the song (and disappear from freeplay) so make sure you have both the base song, and it's erect variant defined.
• You need to have this difficulties defined in the week file for this song and erect song variant for this to work properly.

Card week name (freeplayWeekName)

• This is the text that appears as the week name for this song.
• Base game songs just have there a week number, but your songs can have any text displayable via included font.

One you're done click "Export metadata" to save them as a "metadata.json" file.