Can "item sets" have the shown items be flexible?

When creating item sets, ALL items show up

It's a problem because the entire black market brawlers are on the item sets available to make sets for, and they're not even available anymore

There's also the problem that if you want to make a summoner's rift specific item set, all the crystal scar, howling abyss and twisted tree lines are available to pick even though you've ticked off otherwise.

Can the items shown be more flexible, is that possible?