Actually, I Highly recommend that you open the bleeder valve on the calipers, before you squeeze the pistons back into the caliper body, and drain that used brake fluid out of the system.

The reason why is because the moisture and debris that the fluid collects can and will cause damage to the ABS modulator if it reaches it, and trust me, it will.

You are so much better of setting your risk to 0 for getting contamination into the ABS unit.

BC.