[dungeonguru]

You can peek into the .user file for the community with a text editor to see how it's done. The filename is "COM_5ePack_PHB - Backgrounds.user" and it's normally found for windows installs in C:\ProgramData\Hero Lab\data\5e.

The Background Features are usually created in the General tab of the editor on the Ability subtab. Once created they are bootstrapped onto the background created on the Backgrounds section.

The backgrounds that have 2 variants usually are copies of each other where the feature that is bootstrapped to each one is different and the name indicates a variation.

If you create new backgrounds you'll often have to either copy the Traits, Bonds, Flaws, Ideals and Custom Abilities from the original and make sure they allow your new background or if you have access to the original Traits, etc. you can modify them to include your new background.

Edit:
Slow thought process with coffee this morning. The reason that Sailor and Pirate allow a choice is that the "feature" is actually a custom ability that bootstraps the chosen feature. If you open the file in the editor and choose Pirate you'll see on Custom Ability Count there is a 1 with the name "Feature" typed in. Move over to the Background Custom Ability tab and you can find the two Background "features" that bootstrap the generic ability.

This only works if you have a very simple background - Sage uses this same field to allow the sage specialties and then has to lock down to a single feature bootstrapped to the base background.