You need to change the compressor for one with the propper oil and if you have an expansion valve (TXV) system the TXV should be changed too. The hoses are a differant type for 134 and you need to flush out as much of the old oil as you can.
Unless you need to change the compressor it may not be worth the expense. You could drain the oil and put the correct oil in but this is not recommended for long term as the mixing oils will cause problems.
I doubt they are still allowing any in term refrigerants like Hot Shot for automotive use. We use R416a to replace R12 in refrigeration use, but it is not approved for automotive use. Mainly because it is a blend and needs to be charged in liquid state or the blend will change.
