Nobby
Those extinguishers are rated at 350psi & usually pressurised to 200psi when full of CO2 – I was always nervous of the plastic bottle/sprayer solutions due to the pressures.
I have & do intend to let the air out after each use.
Thought your pressure rating was a bit conservative so I did a bit of research into the pressures involved in these fire extinguishers. Found this info from http://www.fireextinguisherguide.co.uk/types-of-fire-extinguishers/co2-fire-extinguishers/
CO2 extinguishers stores carbon dioxide gas under great pressure (55 bar or 825psi), where the gas becomes a liquid. When you operate the fire extinguisher levers, the pressure is released, the CO2 pressure is reduced by the diffuser (horn) and expands back into a gas, rapidly cooling the surrounding air.
So going by that I think pumping it up to 1 or 2 hundred psi won’t be an issue!