Adding bleach to a tint isn't really advisable. Bleach breaks down pigment, Highlift tint has pigment, so what will happen is the bleach tries to eat away at the tone in the colour, and the tint tries to fight it off. But because you've essentially got bleach and 12% in the bowl, the bleach wins the fight. So what you'll end up with is a really foamy weird coloured cream to apply to the hair that's already fought off a chemical reaction which in turn won't oxidise for much longer, because its exhausted from the fight.
If its a level 10 you're trying to achieve I'd say bleach and tone.
If you didn't want to use bleach for whatever reason, then I'd try 10/1 + 10/86 with 12% instead of the Highlift ranges.
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