Method to free up timer and redefine ISR used by delay()/millis()/micros()

For my particular application, I need to free up an available timer used by delay()/millis()/micros() for another purpose while retaining the use of delayMicroseconds() which is not used by a timer along with placing my own code in the particular ISR thereof and I am looking for a method to do so.

Start by locating the implementations and timer/ISR entry points for delay(), millis(), micros(), and delayMicroseconds(). Determine which timer is used and whether the requested freeing and redefinition behavior can be specified without a board-specific scope; done would require a clearly defined method that preserves delayMicroseconds() while allowing the other timer and ISR to be reassigned.

Written by the indexing model from the issue text.