The title really. An API script is an ok solution as well.
Like, to the sheet, or just an attribute? You can go to the Attributes and Abilities tab and add an Attribute named whatever you like with any value you want, but unfortunately, it won't show up on the Character Sheet, although, it can still be referenced from the character sheet like any other attribute.
You can also take the html and css code then plug it into the customize sheet selection. This will let you add the attribute to your sheets for that game.
To set an attribute on a whole bunch of characters at once you can (as a pro subscriber) use the API script ChatSetAttr too.
Ziechael said: To set an attribute on a whole bunch of characters at once you can (as a pro subscriber) use the API script ChatSetAttr too. This was exactly what I was looking for. Thank you. Ps. Apparently it wasn't obvious from the title that I didn't want to add the same Attribute one by one to each character. I need to pay more attention to my writing in the future. Thanks for SFX and Pat for trying.