a/c conversion question r12->134a ->r-12?

[Richard J. Andrews]

it has been brought to my attention that the r-12 will work with 134, just
the 134 oil is not
compatible with r-12, now if i try 134a with the current oil and decide
it's not acceptable cooling will going back
with r-12 seriously screw things up? i guess i'm asking if using 134a w/12
oil and deciding to go back
will i need a flush due to the 134a containating the oil?

TIA!
-rich
'86 4kq