Mix'n match CH inhibitor?

If it's such a big problem, you could connect a hose to it from the mains, via a pressure reducing valve (very important that) and a pressure gauge that is accurate. Maybe remove a rad to connect hoses. Run water at, say, 1 bar, up the flow & down return and to drain. Open & close valves on rads to ensure they get a thorough flush through. Half an hour or an hour should dilute the existing inhibitors to the point that only a homeopath would claim they'd have any effect.

Shut drain valve, shut inlet valve, remove hoses. The system is full of clean water. Re-fit rad. Pour inhibitors of choice into empty rad, fit & close air vent, open rad valves, vent air, top up pressure.

You'll get a small volume of air coming out of solution when the boiler heats the water up. Maybe heat the system up & vent this before adding inhibitors into the empty rad; this will minimize the depletion of the oxygen scavenger chemicals.

Assuming it's a sealed system, that is.

ROFL excellent I will need to remember that phrase.