 Independent tagged axiomatization

In a conservative language extension, attach a fresh nullary predicate $P_i$ to the $i$th axiom $A_i$ and use a self-indexing copy of $P_i\wedge A_i$. The fresh tag makes each new axiom independent of all the others, while forgetting the tags recovers exactly the original-language consequences. The Craig trick makes the resulting axiom set decidable.