The rules look great. You've put some work into the design!
Some comments:
"Legal and illegal ball potting" (p.3) - This section doesn't clarify what happens if you call one ball, but sink multiple balls. Do the uncalled balls come up? Or all the pocketed balls?
What if you call multiple balls but only make one?
"Bring a reservist into play" (p.3) - I think this section should clearly say that the balls are recruited in order from lowest number to highest, unless they were re-ordered. (Alternatively, a simpler option would be to let people recruit any ball.)
"A reservist cannot be placed on the half where the enemy King is located." (p.3) - I don't think I like this rule. I can see the benefit of stopping the recruited ball being placed next to the king for a dead combination/carom, but it makes the rules complex. If the rule was simply you used your original half of the table, the opponent has a tactical reason to keep his king in his half, and you have a tactical opportunity to get the king into your own half. Then if you do recruit a ball and freeze it to the king, the king has the next shot and can get out of the situation.
"The wall The 8-ball ... cannot be used in combinations or jumped over" (p.4) - Again, I can see the reason for this, but it does make the rules more complex, so my view is the rules might be better without these restrictions (and you might make jumpshots illegal anyway.
(I do like the line "The 8 is the wall and cannot be jumped over, you fool."!)
" -The Saboteur can also take on the role of the Assassin.
- With the Saboteur, you cannot both sabotage and pocket a ball. You need to call one of them."
Are these rules necessary? (As usual, I'm against unnecessary complexity!)
Where you talk about which ball can pot which, it may be worth stating that a ball can legally hit and move a higher-numbered ball from the opponent's group, if it doesn't pot it.
For the simple game, 4 points feels very low. At most, people can only buy 2 balls.
Another thought that occurred to me: Alternative names for the kingslayer: "Hangman" or "Executioner". (Maybe we discussed these before?) I think both have interesting and slightly sinister connotations that give them added 'personality'. It also makes sense that you'd know who the hangman is, but the assassin would be a secret.