What will come in place of the question mark ($?$) when $+$ and $-$ are interchanged and 5 and 18 are also interchanged in the given expression?
$$5-18+12=?$$

Following the instructions, let's substitute the operators and numbers:
* Interchange $+$ and $-$ $\to$ '$-$ ' becomes '$+$ ' and '$+$ ' becomes '$-$ '
* Interchange 5 and 18 $\to$ '5' becomes '18' and '18' becomes '5'

The new expression becomes:

$$18+5-12=?$$

Applying the order of operations:

1. Addition: $18+5=23$
2. Subtraction: $23-12=11$

Therefore, $?=11$.