How to lock a DFF segment at invoice line level in AP

Summary: In the client's setup there is a flexfield segment at invoice line level, which should be locked, once a line is marked for being transferred to an external receiver. (This mark will be set by a custom program using REST API for update of the transaction line).

Via personalizations you can lock a DFF segment based on a value in one of the standard fields at line level, but not based on the value of another DFF segment. Are there other options than using a standard field?

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