Slime gave a tyranid monster +1 damage in the shooting phase. It cost 2 CP. But the neat thing about it was, it was used "In the shooting phase" so you could wait until you saw how many wounds / failed saves you generated. Now you use it "At the start of the shooting phase". 2 CP is alot to spend on a weapon with no AP. Still good for exocrines, just not flyrants or carnifexes.
the commissar example would also be illegal, yet the designers themselves fielded an axe commissar as part of an event IG list. Also the DC explicitly uses an autarch example that would not be legal otherwise