Two-qubit depolarizing error convention in Stim

Question

In the definition of two-qubit depolarizing error in Stim, it is defined that operations such as $IX, XX, YI$ (excluding $II$) act with a probability of p/15, while $II$ acts with a probability of 1-p. Now, I want to use two-qubit depolarizing error where operations such as $IX, XX, YI$ (including $II$) all act with a probability of p/16. Is it possible to achieve this kind of noise using Stim?

Answer 1

If you want to use a depolarizing probability $p$ that includes $II$, multiply $p$ by 15/16 before giving it to stim's DEPOLARIZE2 instruction. (By 3/4 for DEPOLARIZE1.)

As you note, Stim's convention is that the $II$ case is not included. To avoid confusion over what a stim circuit does, this can't be configured. You can only convert into and out of the convention.