I agree this is another money grab by dupont or whomever. If you follow the patents , patent expiration and regulation changes by date it seems more corrupt than environmentally friendly. I'll stop there.

As for the Y1234 vs R134a, The small amount left in the hoses should not make a difference.

If I remember correctly Y1234 is a low pressure refrigerant so make sure the guages will read the pressures needed for a proper charge and go to town.