I'm not sure what the Penrite strips actually test. AFAIK the only real issue with old coolants is degraded corrosion inhibition. The various anti-freeze and anti-boil additives break down much more slowly than the corrosion inhibitors added to coolant additive.
If you follow standard practice and replace your water pump every time you replace a timing belt, you will never encounter the effects of degraded coolant unless you capture your coolant and poured it back in or something.
If you fill your cooling system with plain water, you can do your normal driving as long as your cooling system is in good order. Just don't go towing your boat over the mountains
Cooling systems are (mostly) over-engineered so they can deal with extreme temperature situations. Taking that into account I once drove my old Accord hundreds of kilometers with a punctured radiator but loosening the radiator cap and turning the cooling system from pressurised to atmospheric. As the leak was high up I didn't lose much coolant once the level in the radiator dropped to where the hole was.
Of course by doing that, the temperature gauge will happily show half way while the system boils dryso you need to check how much water is left in the radiator every now and then.
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