revenue reversal rule field

Summary:

in AR there's field 'Revenue Reversal Rule'
with values: LIFO, Prorate, Unit

my question, how to specify the value of that field for Credit Memo that comes from Subscription?
I expect there's a specific field on Subscription that can be used to specify that field, so far I could not find that field

previously have asked SR, and SR said not supporting customization

please advise

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