I'd like something already bootstrapped to show up in a chooser
 

In Dark Heresy, skills can be either basic or advanced. Basic skills can be used untrained, advanced cannot. I currently have my game system set up to bootstrap all the basic skills to every character.

Every career offers 0-3 pairs of skills to choose between as your character's starting skills. I've been using choosers for these selections, since each pair is independant of the others, and exactly one choice must be made from each pair. However, some careers offer basic skills among their options - selecting them would add a tag to show that the skill is now trained. However, because the skills have already been bootstrapped to the character, they don't show up for selection in the chooser.

Do I need to re-write the mechanics of skills, making their uniqueness more like d20, where a special unique tag is added? Or is there a better way to handle this?

BTW, I don't want advanced skills to show up in these choosers if they're already bootstrapped from another source, but I think I can handle that by checking that whatever is allowing skills to be doubled up only allows basic skills to be doubled up.

I assume you are using "enmasse" to add all of the basic skills. As part of that, you must also assign an auto-tag to each basic skill that identifies it as the one that is auto-added.

Then you need to make all basic skills NON-unique. That will allow the user to add them again via the choosers. Within a component Eval script for basic skills, you can distinguish one of the auto-added skills from a user-added skill, with the latter assigning the "trained" tag to the former.

You *can* make sure that basic skills don't show up when they are already selected by the user. It will require only a little bit of work. Define an identity tag group on the basic skills called "UserSkill". Using a component Eval script, each user-added skill must forward the tag to the hero. You can then use the "denytags" mechanism on the choosers to preclude any skill that already exists within the hero. The denytags mechanism is a special application of the "tagmatch" target reference, and it omits any thing from selection that shares a tag in common with the container.

You can use this exact same technique for advanced skills to make sure they only get added once by the user. The only difference is that all advanced skills will forward the identity tag to the hero instead of just the user-added ones.