I'm not sure I have the right end of the stick, but doesn't the condenser/receiver dryer come pre-charged with desiccant?

It might come pre-charged with desiccant but that doesn't help if I can't get the old condenser off to install the new one.

I have a new brainwave to research: If the desiccant adsorption process extracts water from the environment, then as the process can be reversed as was suggested by heating it in an oven, could the process also be reversed by reducing the relative humidity of the environment to near-zero?

If that is so, there might be an alternative way to re-activate the desiccant by putting the system into a vacuum condition for several days so that the existing desiccant releases its previously adsorbed water content. I would propose to evacuate the system and seal it for 24 hours. It should hold a vacuum, except for any water vapour that might be released by the desiccant. I would then re-evacuate it and seal it for another 24 hours, then repeat for a few cycles. After this I might have reserve desiccant capacity and can then charge the system with refrigerant and be fairly confident that it will be stable and work satisfactorily for another 10 years.

Any thoughts on this?

Ahh yes, indeed. Moisture should boil off under vacuum, so yes - a long term vac will probably get you some capacity back in the old desiccant.

Pic taken this morning, shows system has been holding vacuum since yesterday. It has been about 23 hours since I started the program of extended vacuum exposure to hopefully regenerate the desiccsant.