About character pool spawn options

Is there some way of ensuring that the characters can spawn as rewards for missions or scans, but can't be acquired via standard recruiting? I saved the character appearances of my final squad and a couple of notable troopers that died along the way in my previous playthrough and liked the idea of them appearing as special Soldier rewards for scanning, guerilla ops, hired at HQ or the Black Market, etc.

Instead, two of them showed up in my initial set of four rookies, which means I've probably got a couple more of them waiting to be recruited on the Avenger. Kinda makes it less of a surprise "hey, I know that guy!" thing and more of a "oh, you again?" thing.

Any idea how to fix this? If I set them to spawn only as VIPs, does that also mean they can appear as hirelings or rewards? I know Beaglerush has hired a few custom characters in his campaign, but I'm not sure if he had them set to appear only as VIPs, as VIPs and Soldiers, or what.