Am I correct in thinking that the PCB hole that can be seen on the 8825board next to the chip and two surface mount parts near the pot is the same access as the hole on the older 4988 board in that gives access to the Voltage setting for the current level? I am using that on the older devices to drop the current when the motor is not being used and does not need any significant holding current to prevent unnecessary current draw through the motor. Doing this also, I believe, maintains the micro step information in the chip instead of resetting it. I am driving 5 stepper motors and control all of them this way. I attach a wire to the board hole and pull down on it thru a 200 ohm resistor which drops the current to some very low value. Otherwise I would need a much bigger power supply and would generate a lot of unnecessary heat in the motors, drivers, and power supply.
The DRV8825 and the A4988 stepper motor drivers are similar in many ways. You should be able to compare the schematics and datasheet provided on the DRV8825 product page (under the “Pictures” and “Resources” tabs respectively) to the A4988 and confirm it will work the same. That general approach should work, but note that the relationship between reference voltage and current limit differs between the two drivers, so you might ultimately want to use a different value for the pull-down resistor.
Also, there is a previous thread you might find useful about modifying a DRV8825 to allow a microcontroller to set the current limit.