Great question! For clarity’s sake, let’s call these type of abilities specialties.

Short answer: Yes and no. You can to a degree but there are restrictions.

Long answer: There are a few conditions with regards to this. First, the specialty needs to have been introduced in AtLA or season 1 Korra; as such, something like lavabending would not be allowed since its not introduced til a later season, or even the “compressed” fire bending we first see in AtLA with sparky boom boom man Combustion Man since the ability is not explained til later in the Korra series.

Secondly, there need to be plausible reasons (which as per the rules excludes prodigious ability) for a person to have the specialty, keeping in mind that all specialties must require honed, specialty training. For example, we know that as far as season 1 Korra, the only metal benders are earthbenders with police training. Therefore, all metal benders need to either be active or retired police officers.

Third, you would have to work closely with either Gia or myself to make sure the specialty you choose won’t unfairly skew the power balance — for instance, blood bending is by its nature godmoding since it moves the opponent without their consent. If your character passes the first two conditions, we would have to temper the strength of the specialty to a reasonable level for your character’s age, experience, history, and board balance; additionally, we would monitor your use of the specialty in-game to make sure that you’re not using it unfairly.

If you have more specific ideas for your character that you want to discuss, please feel free to PM one of us with the details and we can go into more depth.

Does this help?

It helps a lot, thanks! I'll be sure to PM you to go more in depth of what I'm thinking of.