Large Water Changes When Playing With Water Chemistry

I was wondering if any of you take any special precautions when adding
tap water that has different chemistry than the tank water.

I'm assuming it would be important to either *not* do a large water
change *or* to add water very slowly, over a period of time when one
is doing say, CO2 injection, or is using driftwood, coral, etc. to
alter water parameters.

Is this true, or is whether you can do it based on certain guidelines
re the extent of chemical difference or fish species involved?

TIA