If you need to access the coolant side, yes you will need to drain it down to below the exchanger level, the answer is no with reservations if you have to access the raw water
side, if the stack seal is maintained which generally only happens in older poorly maintained engines. My advice would be to drain down to below the exchanger level using a clean bucket to collect the coolant any lost
coolant volume can be made with potable water
without any ill affects until in a position to get the real mc Coy.